Water resources, whether exceeding per capita water abundance thresholds or below water scarcity thresholds, are health determinants within small island developing states (SIDS). Thresholds indicate water stress vulnerability in SIDS, but underestimate the physicality associated with a lack of water. The objectives of this study were to capture the main challenges of consistently meeting water demand in SIDS and to present their intersection with certain diseases or factors associated with specific health conditions like dengue fever, gastrointestinal disorders, dehydration, and malnutrition. This review utilized archival evidence to categorize the challenges undermining water availability in SIDS with the view that these issues present or exacerbate health outcomes. Seasonal rainfall variations (73%), inadequate distribution infrastructure (64%), saltwater intrusion (61%), contamination (58%), human-induced watershed change (19%), and sea level rise (17%) were identified from 108 country-specific sources as challenges to consistently meeting water demand by 59 SIDS. Any water stress indicator must consider that it is contingent on its human burden. These challenges affect food security through agricultural drought and soil salinization, and the proliferation of vector-borne and sanitation-related diseases across SIDS. This review is the first step in determining the human health burden of water insecurity in SIDS.
Environmental properties, resource protection and distribution infrastructure determine water security in SIDS.
Rainfall variations and saltwater intrusion affect water resources in >60% of SIDS & threaten food security.
Seasonality, insufficient infrastructure, watershed change, and pollution increase the risk of vector- & water-borne disease.
Accounting for the human burden of climate-associated water insecurity would benefit SIDS.
The question remains, even in the two-thirds of countries whose water resources per capita are deemed adequate, how many persons have access to the theoretical ≥1,700 m3 per year, and how are these disparities impacting the wellbeing of populations in SIDS? This study is presented as an attempt to capture the main challenges to consistently meeting water demand in SIDS as well as summarize the health impacts that these challenges will exacerbate.
Other indices have been developed that, for example, focus on the social aspect of the Falkenmark Water Stress Indicator by applying the human development index (HDI) (Ohlsson 2000), or focus on scarcity as defined by freshwater storage (Damkjaer & Taylor 2017), or indices that focus on watershed sustainability (Chaves & Alipaz 2007). However, these indices fail to account for the burden that water stress poses on human health, either directly from lack of water or by added risks due to water shortage. Furthermore, these indices present a general overview of certain aspects of water scarcity without providing guidance on the source of the issues, their relevance to certain countries, and most importantly, where to target for the allocation of policies and corrective interventions in the face of limited financial and human resources. Such limitations hinder the application of most indices to SIDS and fail to incite action.
Shared geographical, geomorphological, socioeconomic, and climatic characteristics of SIDS have predicted the occurrence of many similarities in issues being faced as a result of water stress and water scarcity. These issues are also among the risk factors that negatively affect human health. Extended dry periods cause droughts across SIDS that can reduce the quantity of water available as well as water quality. This, in turn, can lead to reduced agricultural yield and food insecurity for vulnerable populations, the proliferation of arboviral infections, unsanitary practices, and the concentration of inorganic and organic pollutants in sources of water. In SIDS, drought impacts affected over 7 million persons from 2011 to 2022, compared with the period 1990–2010 where around 3.5 million people were affected by droughts (EM-DAT and CRED 2023). In Papua New Guinea, as much as 83% of food energy was provided by local agricultural and subsistence farming, making the impact of the 2015 drought and the famine that followed unprecedented (Gwatirisa et al. 2017). Household surveys in the aftermath of the 2015 drought revealed that many agrarian households responded by skipping meals, which placed communities at further risk for malnutrition since those communities traditionally have high carbohydrate diets with occasional supplementation of proteins from canned fish and beef (Gwatirisa et al. 2017). The severity of droughts, perhaps, more visibly manifests in low HDI countries or low-income agrarian communities. However, a trend towards increased reliance on imported foods in developing countries, like some middle- and high-income SIDS, has shifted consumption patterns to foods associated with risk factors for certain chronic non-communicable diseases (Belahsen 2014).
Numerous studies also provide evidence of positive correlations between seasonality and infectious diseases (Solomon et al. 2007; Chretien et al. 2015; Lowe et al. 2018). In equatorial and tropical regions, associations of infectious diseases with El Nino events have been made from outbreaks of cholera, dengue, malaria, and other emerging and re-emerging infectious diseases in SIDS (Chretien et al. 2015). Of note, dengue outbreaks in the Pacific and Caribbean have been preceded by dry conditions (Chretien et al. 2015) as water storage with uncovered containers promotes the breeding of dengue vectors, Ades aegypti and Ades albopictus. Furthermore, warmer temperatures, which typically co-occur with droughts in tropical regions, can help reduce the extrinsic incubation period of dengue viruses (DENV) in vectors (Xiao et al. 2014), thereby increasing the transmissibility of the virus. Another arbovirus that shows associations with warmer, drier conditions is leishmaniasis which spreads to humans from sand flies infected by the Leishmania parasite – outbreaks of which have been reported in Barbados and other Caribbean countries (Chretien et al. 2015). Leishmaniasis is typically underdiagnosed due to biting going unnoticed as the sand fly is significantly smaller than mosquitoes, as well as the fact that skin lesions from the more common cutaneous form of the infection manifest weeks or months after bites. The more severe form, called visceral leishmaniasis, may show symptoms of spleen or liver enlargement months or years after appearing dormant in humans (Romero & Boelaert 2010). Like many parasitic infections, the severity of symptoms also depends on immune system resilience which can be contingent on food consumption patterns.
On the one hand, flooding may increase the range of other bacteria in rainy seasons. Paradoxically, droughts and reduced water flow may increase the concentration of these organic pollutants in water sources. Poor access to safe water for drinking and domestic use can lead persons to inadvertently seek out sources with concentrated bacterial populations which causes the human transmission of other infectious diseases. This, coupled with unsanitary practices that are worsened by impromptu water conservation practices, has led to outbreaks of cholera and gastrointestinal disorders in some SIDS. Case in point, a study evaluating the water quality of hand-dug wells in communities surrounding the Artibonite River in Haiti (Schram & Wampler 2018) found that these informal well systems tapped into shallow groundwater systems and were used for drinking and domestic purposes. However, due to connections with contaminated runoff and degraded dissolution pathways of the karstic lithology, groundwater in this area is conducive to high concentrations of E. coli and V. cholerae – mechanisms which have been linked to past cholera outbreaks (Wampler & Sisson 2011). From the sampling of 35 hand-dug wells in this region, 89% were categorized as unsafe by WHO standards for drinking water, due to having over 1.0 cfu (colony-forming unit) per 100 ml of water (Schram & Wampler 2018). Moreover, warmer temperatures that tend to co-occur with dry conditions in tropical zones, facilitate bacterial growth, and lead to resident bacterial populations in contaminated groundwater (Wampler & Sisson 2011). Owning to the karstic topography, the Artibonite River region in Verrettes also has several natural karst springs that are used as water sources for surrounding communities. Seventy-one to 100% of springs sampled had E. coli levels higher than safe consumption levels (Wampler & Sisson 2011). These cases provide evidence of the susceptibility of aquifers connected to permeable formations like limestone or alluvium, to groundwater pollution.
The challenges associated with a lack or shortage of water can incapacitate the development of a country, especially countries, like many SIDS, where purchasing power is highly dependent on efficient utilization of limited natural resources. Desalination has emerged as one of the most prominent solutions to the global water crisis where over 170 countries practice desalination with capacities of at least 100,000 m3/day (Jones et al. 2019). Widely known as energetically and environmentally expensive for having large energy requirements, huge carbon footprints, and large quantities of waste by-products, desalination serves as a solution with a heavy price. Efforts have improved technological efficiency and reduced liquid discharge of desalination plants. For example, reverse osmosis (RO) desalination is preferred for its lower energy consumption than distillation desalination. Similarly, forward osmosis technology has facilitated a novel method for extracting economically viable salts and ions from brine, thereby, redounding in minimal/zero liquid discharge (Panagopoulos & Giannika 2022). There has also been a recent push across many SIDS to promote traditional practices in water management, particularly in the Pacific islands. These practices tend to focus on rainwater harvesting techniques that eliminate or supplement the use of obstructive infrastructures at the community level. These perspectives must be accounted for as they speak to the quality of life lived, measurable only on a scale understood and appreciated by the locals affected. Regardless of the methods employed to provide solutions to water insecurity across SIDS, a classification of the frequency with which each issue arises, and the severity of connected health impacts will facilitate the first step in ultimately determining the burden of water scarcity on health in SIDS. This will better enable governments and stakeholders to assess target areas based on the highest need and the potential impacts to human health. An index categorizing the challenges and health risks will promote visualization of the interconnectivity of each issue and demonstrate that solutions cannot occur in isolation. This is especially true for SIDS where consequences are evident over smaller geographical and temporal scales. Any water stress indicator must consider that water insecurity is contingent on its human burden. This is the first such scoping review presenting the health burdens attached to water challenges for SIDS and synthesizing existing literature on this topic.
The Preferred Reporting Items for System Reviews and Meta-Analyses (PRISMA) were developed to provide a transparent reporting standard encompassing the minimum set of items required for an evidential review of literature, databases, and the evaluation of publications (Page et al. 2021a, 2021b). The PRISMA methodology presents guidelines for the assessment of the trustworthiness and applicability of review findings. A series of steps and criteria by which articles and data should be identified, selected, removed, and included prior to and during review was formulated (Page et al. 2021a, 2021b). It recommends highlighting the reasons sources are moved through to the next stage of review by assigning predetermined eligibility criteria. The PRISMA methodology is extensively used in systematic reviews and critical appraisal of clinical and medical research, as well as in mixed-method reviews of non-health-related interventions.
Although this is a scoping review, the PRISMA methodology for systematic reviews was modified to conduct this study (Page et al. 2021a, 2021b). Two main criteria were developed to evaluate the eligibility of sources retrieved after the keyword searches; whether sources were:
Hosted on, reposted on, or affiliated with international/regional organizations, state-owned news agencies, universities, country governments, and scientific organization websites.
Portals operated by not-for-profit organizations, privately owned developmental agencies, or private news/e-magazine agencies.
Initial keyword searches for each country were ‘water resources [country name]’, ‘primary water source [country name]’, ‘surface water resources [country name]’, ‘groundwater resources [country name]’, and ‘water resource management [country name]’. ‘Follow-up’ keyword searches were done as needed based on information from the initial keyword search or for identifying the challenges to water resource management (WRM) by country. This stage consisted of keywords ‘desalination [country name]’, ‘rainwater harvesting [country name], ‘non-revenue water [country name], and ‘unaccounted for water [country name]’. Since online academic libraries and bibliographic databases are specifically geared towards published articles and studies which are, at times, lacking or not widely distributed in SIDS, record results were minimal after academic libraries were searched. For SIDS, where such information exists in forms such as news articles, unpublished reports, or public announcements, more successful results were yielded from the general Google Search Engine compared with searches of PubMed, Elsevier, and Google Scholar. No filters or limits were applied to the search.
The first checkpoint in the selection process involved identifying material containing information on the keywords for each country or group of countries belonging to the official list of UN and non-UN SIDS, where n = 118 records were identified. Prior to screening, sources were removed if they consisted of duplicates from an original host database (n = 4). Tertiary sources (n = 1), such as online encyclopaedias or primary sources which had irrelevant information (n = 2), were among those removed prior to screening. After pre-screening removal (n = 7), n = 111 records were evaluated through a criteria-based screening process. Materials were deemed to be from knowledgeable and reliable sources, firstly, if categorized as government documents (n = 3), conference proceedings (n = 4), drafted or published commissioned reports (n = 30), peer-reviewed journal publications (n = 21), or book sections (n = 5) on the relevant subject matter. Press releases, maps, and electronic articles were included if they met the first eligibility criterium (n = 36). Due to a paucity of reports and studies in some countries, electronic articles hosted on portals operated by not-for-profit organizations, privately owned developmental agencies, or private news/e-magazines agencies were included if they proved to be the only source of relevant country-specific information (n = 9). Records were removed after retrieval which did not contain relevant information despite matching keyword identification (n = 3). A total of n = 108 sources, comprising published or drafted reports (n = 30), journal articles (n = 20), electronic articles (n = 15), organization webpages (n = 9), repositories (n = 6), press releases (n = 6), book sections (n = 5), blog entries (n = 5), conference proceedings (n = 4), government documents (n = 3), maps (n = 2), an interview (n = 1), a presentation (n = 1), and a pamphlet (n = 1) were reviewed. The reference list for these reviewed sources is contained in the Supplementary Table (Table of Sources Reviewed by Country).
The latest available information used for this study was published or written between 1978 and 2023. Priority was given to information on potable water resources though in some cases potability was not disaggregated from domestic or irrigational use. Water supply facilitated by government agencies or privately-run companies was also not distinguished, although government agencies are largely responsible for water management across SIDS. It must be noted that this review is not an indictment on any government or an assessment of institutional capacity, but a demonstration of the commonality of issues surrounding water availability in SIDS and the human health vulnerabilities these issues exacerbate across countries.
To process the information from the literature that met the inclusion criteria, a binary scheme (‘yes’ or ‘no’) was adopted to assess the information from literature into three separate groups: ‘Natural Freshwater Resources’, ‘Water Supply Source’, and ‘Challenges to Water Resource Management (WRM)’. Within these groups, information was classified into sub-categories, where in ‘Natural Freshwater Resource’ it was determined if a country had groundwater resources and/or surface water resources; in ‘Water Supply Source’, the sub-categories were river intake/catchment, groundwater abstraction, rainwater harvesting, and/or desalination; within the ‘Challenges to WRM’ category, six of the most common challenges were assessed for occurrence or non-occurrence: pollution/contamination, saltwater intrusion, sea level rise, seasonality, human-induced watershed change, and/or supply infrastructure. Furthermore, the primary source for meeting water demand within the ‘Water Supply Source’ category was identified from the literature reviewed.
Given the limited freshwater resources, 93% of the 59 countries rely on more than one source of water with 53% of countries using three sources, 36% relying on two sources, and 5% relying on four sources (Figure 3(b)). Only 7% of SIDS (Bonaire, Curacao, Dominica, Montserrat, and St Lucia), all of which are Caribbean countries, rely on one source of freshwater to meet internal water demand. Only Singapore utilizes reclaimed water (Lee & Tan 2016).
Groundwater is the most tapped-into internal freshwater resource with 85% of SIDS utilizing some quantity of this resource, however, river/runoff catchment serves as the primary freshwater resource in most SIDS. Rainwater harvesting, which depends on total precipitation and the location of countries within climate zones, is the 2nd most utilized water resource in SIDS (64%). According to the Koppen–Geiger Climate Classification, 53 of 59 SIDS are within the tropical climate zone with significant annual precipitation levels. Moreover, the majority of those SIDS have a tropical rainforest climate characterized by at least 60 mm of rainfall per month. Yet, rainwater harvesting is used as the primary resource in only a few SIDS (10%). Rainwater harvesting poses challenges due to the assumption of point-of-use water treatment, as well as the fact that improper storage increases the risk of contamination. Additionally, with shifts towards longer and more severe dry periods associated with climate change, this may not be a reliable source if there is no appropriate infrastructure for long-term water storage. However, once the potential threats are mitigated, rainwater is a viable and cost-effective solution that may be applicable to the 90% of SIDS that have seasonal rainfall to support it.
Of the four main sources of water, desalination is the most underutilized method for meeting water demand with less than half of SIDS (44%) using this energetically and environmentally expensive resource (Figure 4). The 12 countries that rely on desalination as their primary water resource are notably water stressed according to the Falkenmark Water Stress threshold and are within the high-income gross domestic product (GDP) bracket. Desalination can provide water security at the expense of water quality, or human, and environmental health. As previously noted, desalination consumes a large amount of energy, produces a large quantity of CO2 emissions, and has highly concentrated brine by-products. Brine from desalination is often discharged into coastal environments, furthering degrading ecosystems on which many communities and economies across SIDS depend for livelihood and subsistence. Reverse osmosis desalination plants are the more commonly noted mechanism of desalination utilized in SIDS and are preferred over other methods due to the lower energy requirements compared with other types of plants. Other concerns have been raised about the impacts on air quality for surrounding areas (Panagopoulos & Haralambous 2020) as well as the depletion of underground brackish aquifers. Reverse osmosis, though less expensive to run, is more efficient at desalinating brackish water than seawater. Consequently, some plants tap into brackish water from coastal aquifers or from shallow lenses to supply freshwater at a lower energy price tag. The Republic of Marshall Islands primarily relies on rainwater harvesting to supply freshwater; however, this is supplemented by reverse osmosis desalination plants – 86% of which are located at the centres of the islands (MacDonald et al. 2020), where lens would be thickest in these atolls. Based on this pattern, there are serious concerns about the upconing of seawater at the islands' centres as a consequence of the over-pumping of brackish water for desalination, which would present a risk of soil salinization. From a survey of 298 households and 16 focus groups, persons in the Marshall Islands expressed a need for balancing desalination technologies and the use of traditional methods for rainwater harvesting, with emphasis on the potential loss of the traditional use of hollowed-out coconuts to collect rainwater [Mammaks] which has been largely replaced by large tank storage (MacDonald et al. 2020). Upper-middle-income to high-income countries may have the financial capacity to explore the use of minimal/zero [brine] discharge desalination technologies that reduce environmental consequences while monetizing mineral and halide by-products through the use of renewable energies and forward osmosis desalination (Panagopoulos & Giannika 2022). However, solutions must caution against the risk of maladaptation and temper technological advancements with local perceptions to ensure that sustainability does not compromise the lived experience for populations in SIDS.
Challenges to WRM in SIDS
Seasonality, which includes the impact of drought, changes in mean rainfall and reduced runoff on water availability, presents issues with meeting water demand in 73% of countries and is the most commonly occurring issue in SIDS. Obsolete or insufficient water supply infrastructure accounts for significant water loss in 64% of SIDS. This is succeeded by the compromising of groundwater resources from saltwater intrusion (61% of SIDS) leading to well abandonment and/or expensive water treatment solutions. Contamination of freshwater resources by improper waste management has been reported in 58% of countries. Human-induced watershed change refers broadly to human activities that have a more negative impact on watersheds such as land use change, topsoil erosion associated with urban structures, and other activities that inhibit environmental requirements in watersheds. Improper land usage within watersheds has been observed to compromise groundwater and surface water resources in 19% of SIDS, while sea level rise has definitively affected water resources in 17%.
As the most tapped-into freshwater resource in SIDS, the typical challenges associated with groundwater abstraction affect a high proportion of countries, the impacts of which would be heightened in the 15 countries (25%) that rely on groundwater as their primary water resource. Of the SIDS that implement groundwater abstraction, saltwater intrusion has been identified in 36 countries (Tables 1 and 2). Saltwater intrusion refers to horizontal and/or vertical encroachment of coastal waters in near-coast aquifers and can be, at times, be attributed to natural phenomena like eustatic or isostatic changes in sea level, and hydraulic interface dynamics between denser seawater and fresher groundwater. However, more times than not in human-dominated biomes, saltwater intrusion is mainly the result of over-abstraction, contributing such a significant degree to the lowering of the water table and the buoyancy at the saltwater-groundwater boundary that changes due to natural phenomena become obscured. Notwithstanding the foresaid, in a subset (nine countries) of SIDS whose water tables were ≤5 m below land surface, saltwater intrusion is explicitly compounded by sea level rise due to fresh/brackish water occurring as shallow lenses in coastal aquifers. More troubling, groundwater abstraction is the primary water resource in four of those countries. For Barbados, Kiribati, Maldives, and Tuvalu, where saltwater intrusion is a clear consequence of both over-abstraction and sea level rise, the issue is further compounded by pollution of groundwater by improper waste disposal. Contamination of groundwater has been identified in 17 other countries that are also faced with saltwater intrusion.
Unhighlighted cells with ticks represent country usage of the columnar means of water supply, while primary means of supplying water are shown in cells highlighted in grey with the tick symbol. The primary water resource was not identified in the Federated States of Micronesia, Sao Tome and Principe, French Polynesia, and Singapore. References from the scoping review of 108 sources of primary and secondary information are in a Supplementary Table (Table of Sources Reviewed by Country).
Tick symbols within the grey cells indicate the occurrence of the columnar challenge. Singapore was the only small island state to experience none of the commonly reported issues faced by the remaining SIDS. References from the scoping review of 108 sources of primary and secondary information are in Supplementary Table (Table of Sources Reviewed by Country).
Surface water resources are used as the primary water resource in 28 countries with 22 mainly dependent on river intake and six mainly reliant on rainwater harvesting. Eighty-six percent of those 28 SIDS experience fluctuations in monthly rainfall and runoff, and evapotranspiration rates that impinge water supply logistics, resulting in planned and unplanned water shortages (Tables 1 and 2). In five SIDS, the quantity and quality of these water resources are also at risk from human-induced watershed change. Dominica and St Lucia are particularly at risk from seasonal changes in rainfall since river/runoff catchment is their only internal source of freshwater resources. Dominica and St Lucia have also had challenges with pollution of their water resources and human-induced watershed change, respectively. While the literature review has identified seasonal fluctuations as an issue in 73% of SIDS, it is implicit that water security in all countries that utilize surface water is susceptible to climate change through variations in precipitation and evapotranspiration.
Pollution of water resources affects ground and surface water resources in a high proportion of SIDS, regardless of income-bracket and HDI. This essentially stems from fragmented and insufficient management of waste and wastewater disposal and treatment in most SIDS. In fact, despite improvements in the coverage of wastewater disposal facilities in the Caribbean, only 53% of populations are connected to septic tanks, while 25% are connected to sewer networks and 20% use improved latrines (World Health Organization 2022). The use of improved latrines can be an appropriate form of in situ waste disposal and treatment; however, this method increases susceptibility to groundwater contamination if not properly constructed and maintained or if sited above permeable formations. Even in the proportion of populations connected to septic tanks and sewer networks, there is an even higher risk of improper wastewater treatment after collection. In the Caribbean, most wastewater treatment facilities have attained only primary level treatment – meaning, wastewater treatment only consists of the removal of solids without the removal of biological material. Furthermore, many facilities then combine these connections with stormwater discharge and practice long fallout discharge into oceans. Poor maintenance further exacerbates the risk of surface and groundwater contamination from these systems. Many solutions have been explored to improve wastewater treatment including nature-based solutions like repurposing wetlands for wide-scale treatment. Other solutions take a multifaceted approach under integrated water resources management targeting policy, and government and private partnerships. One of the most effective solutions has been water reuse, which has been employed by certain sectors for industrial and recreational purposes and can prove to be a solution for water-stressed SIDS. Only Singapore has progressed towards the use of treated wastewater for domestic purposes, which supplies 40% of their water needs. Interestingly, Singapore has the most diversified means of supplying water of all SIDS and is the only one that has no reports of being affected by any of the common challenges to WRM.
According to the World Development Indicator for internal freshwater resources, about 60% of 27 SIDS have >1,700 m3/day/capita available for water consumption (World Bank 2023), giving the, arguably erroneous, impression that inadequate water resources are not a concern in the majority of SIDS. However, as proven by reported water shortages plaguing countries with >2,000 m3/day/capita (World Bank 2023) (Table 2), adequate water resources do not directly equate to water availability. One major shared reason for this is essentially limited and/or obsolete water supply and distribution infrastructure – a feature underpinning economic water scarcity. For some of the other countries with <2,000 m3/day/capita, water distribution infrastructure further compounds the issue of inadequate freshwater resources, presenting the second most frequently occurring challenge to water provision in SIDS with 64% of countries indicating as such. Infrastructure is a confirmed problem in 14 of the 21 Pacific islands (67%), 18 of the 30 Caribbean countries (60%), and 6 of 8 SIDS from the Atlantic, Indian Oceans and Mediterranean and South China Seas (AIMS-75%) (Table 2). Poor distribution infrastructure includes insufficient infrastructure – normally occurring when local population growth exceeds the existing domestic irrigation capacity and is a feature of urban sprawl and densification – and faulty/obsolete infrastructure – normally maintenance and material deficiencies (leaky and broken pipelines) resulting from, and in, failures in adjusting to turbidity and pressure gradients. The latter is one contributing factor to losses in piped water, termed non-revenue water or unaccounted-for-water as this water has been produced but the loss cannot be metered, while the other contributing factor to non-revenue water is water theft from illegal bypassing of water meters. In some countries the exact amount lost to non-revenue water has not been definitive; however, in 13 SIDS, the value has been as low as 5% (Singapore) to as high as 80% (French Polynesia and Solomon Islands) (SOPAC and ADB 2002; AFD 2018; Public Utilities Board 2022), with eight countries reporting that ≥ 50% of water produced is lost as non-revenue water.
Overall, 58 of the 59 countries have indicated that their WRM strategies are undermined by at least one of the six main challenges associated with maintaining stable water supply and demand logistics. While issues stemming from seasonality and sea level rise are direct outcomes of weather extremes and climate events, other common issues, like human-induced watershed change, contamination of resources, inadequate supply infrastructure, and saltwater intrusion are challenges that will worsen the burden of climate variability on providing adequate and improved water. For the purpose of developing a tool to capture the most relevant water issues connected to human health in SIDS, further research will need to be done to expand on the risk factors associated with the challenges affecting the highest proportion of SIDS – those being, seasonality, supply infrastructure, saltwater intrusion, and contamination. Human-induced watershed change and sea level rise are important; however, they are not typically the main issues preventing water provision, as indicated by their lower reporting. These two issues serve to worsen the impacts of the other four main challenges. As such, focusing on the challenges affecting over 50% of SIDS can account for watershed management and sea level rise mitigation. In the subset of countries affected by seasonality, pollution, and insufficient supply infrastructure, the burden on health would be reflected in the risk for infectious disease transmission, specifically for vector-borne diseases like dengue (endemic and re-emergent in all three SIDS regions), cholera (particularly in countries with historical local spread), and gastrointestinal disorders. In countries challenged by both seasonality and saltwater intrusion, the health burden may be more noticeable over longer-term incidence of undernutrition from losses in agricultural production (particularly in rural agrarian communities). This may also be a partial contributor to overnutrition, as populations rely more heavily on imported food items, a trend which can extend past non-drought periods. These health outcomes have a gender component as certain groups are more vulnerable to adverse effects from food insecurity and sanitation-related infectious diseases. This cataloguing of challenges to WRM strongly suggests that climate and weather phenomena continue to increase susceptibility to water insecurity in 98% of SIDS.
Malnutrition and dehydration as prolonged impacts of water insecurity on food security
While middle- to high-income SIDS may observe little change in direct water consumption during water shortages, in low-income SIDS, the threat of dehydration during prolonged droughts remains a critical issue (FAO 2021). During the summer months of 2022 in Kiribati, the long-term drought brought on by a severe El Nino event presented with an increase in infectious diseases and fears of dehydration impacting childhood education and development (Chudeau 2022). Apart from notable extremes, dehydration is seldom the result of failure to meet water demand, however, there are implicit relationships between limited freshwater and lowered water intake. Within groups with co-morbidities, such as obesity, respiratory diseases, and diabetes, and in groups exposed to risk factors, reduced water intake can exacerbate certain adverse outcomes. In SIDS, the risk factor of particular relevance is heat exposure, as persons are exposed to higher temperatures due to employment in agriculture and construction which can involve spending up to two-thirds of each day outdoors (Bureau of Labor Statistics 2020). Dehydration has been identified as a risk factor compounding the onset of kidney injury in construction workers also exposed to higher-than-normal temperatures in Saudi Arabia (Al-Bouwarthan et al. 2020). Dehydration has also been linked with small but significant degradation of cognitive function, especially during tasks requiring attention, executive function, and motor coordination (Wittbrodt & Millard-Stafford 2018), as well as an increase in neural activation leading to greater impairment in visuomotor accuracy (Wittbrodt et al. 2018), which places farmers and construction workers at an added risk for occupational accidents as higher temperatures will result in more water loss and the need for more water replacement.
The rising threat of soil salinization
In islands with shallow water tables or arable land above coastal aquifers in the Caribbean and Pacific, unsustainable agricultural practices and sea level rise conflate to cause capillary leaching of saline water throughout soil systems. The degradation of soil systems due to the salinization of agricultural lands constitutes a remarkable crisis to agricultural productivity in small islands, particularly in the Pacific (Solomon et al. 2007). Given that around 80% of Pacific islanders subsist from their own small-holder agricultural produce, the occurrence of saline intrusion in arable land poses yet another imminent health threat to food systems in this region (Georgeou et al. 2022). As crops have set salt tolerances, saline intrusion may reduce thriving in salt-sensitive plants, such as citrus, potato, and beans (Beltagi et al. 2006; Lantzke et al. 2007) meaning that, at least, a subset of the 61% of SIDS already observing saltwater intrusion are extremely susceptible to yield losses as a result of salinization. In addition, increased salinity induces changes to soil physiochemistry such as permeability, flocculation by salt aggregation, and can lead to poor soil drainage depending on soil type (e.g., increased salinity in clayey loam) which in turn may result in increased runoff and erosion (Pearson & Bauder 2006). In Bahrain, a small island state within an arid climatic zone, degradation of agricultural lands located away from the coast has been observed that was likely attributed to both farm management practices and groundwater quality deterioration (Abahussain et al. 2014). Storm surge-affected areas within the Bahamas showed three times more salinity than in areas unaffected by surges (Moxey 2018), indicative of the surge-induced rise of water tables in near-coast areas. Attempts to achieve universal food security, healthy nutrition, and sustainable agriculture in the near to intermediate future will be exceptionally challenging for countries like Kiribati, the Federated States of Micronesia, and Tuvalu, which, in addition to saltwater intrusion compounded by sea level rise (Table 2), may note lower groundwater recharge rates due to observed and projected reduced precipitation (World Health Organization 2015).
Droughts, water shortages, and infectious diseases
Prolonged water shortages, as a universal public response to the compounded effects of meteorological and hydrological droughts, are linked with more frequent and widespread outbreaks of infectious diseases. This arises from improper sanitation practices prompted by attempts to regulate and conserve limited water supply, as well as improper domestic-level water storage practices, especially within urban communities. In SIDS, where the majority of islands are located in tropical climates, the more common expression of drought occurs over 3- to 6-month intervals, whereas in arid climates, 24-month droughts are more common. The extent of (meteorological) drought periods can determine whether a country may experience seasonal water shortages or suffer from chronic water deficit, which in turn determines the types of public response, such as having enclosed tanks for long-term water storage or impromptu water storage containers. The latter, typically associated with short-term droughts, occurs as containers are repurposed for storing water resulting in large quantities of uncovered and partially covered stagnant water in urban communities. These conditions favour the proliferation of mosquitoes in settings favouring the transmission of the pathogens they carry. In a study determining the impact of climate on dengue risk factors in Barbados, Lowe et al. (2018) found that while excess rainfall preceded dengue outbreaks over short 1–2-month lead times, drought conditions preceded outbreaks over longer lead times of up to 5 months. Pervasive losses of produced water, as experienced in 64% of SIDS, reveal debilitating inadequacies in water supply and distribution infrastructure through worsening the burden of providing adequate water to communities during drought times. The 43 SIDS that have confirmed challenges with rainfall variability are all among those vulnerable to experiencing these impacts, 31 of which have notable issues with obsolete and/or insufficient supply infrastructure further increasing the likelihood of improper water storage and, correspondingly, of mosquito-borne disease outbreaks.
Furthermore, drought conditions can lead to lowered water quality owing to the associated reduced dilution from lower precipitation and increased concentration of contaminants from the higher evapotranspiration rates that tend to co-occur with seasonal rainfall reduction (Wright et al. 2014). Seeing that pollution of water resources is being experienced in more than half of SIDS (56%), more frequent droughts over longer periods – as expected to occur with climate change – will worsen the concentration of inorganic and organic toxins in these already compromised surface and groundwater systems, and with it, the presentation of more sanitation-related infectious diseases and possibly, over a longer term, in the certain non-communicable diseases through the release and concentration of carcinogenic industrial waste (Evans et al. 2019). Unfortunately, like so many other potentially climate-sensitive diseases, in SIDS there have been no studies attributing certain cancers to water pollution by hazardous industrial waste, and even more concerning, none on how meteorological factors contribute to worsening the development of these conditions. The recurrent, and climate-controlled, threats to human health due to the consumption of water from contaminated sources will likely be of greater severity in the lower-income countries that are already at a disadvantage, where as much as 44–83% of populations in these SIDS do not have access to basic sanitation services (FAO 2019; World Bank 2023).
Several limitations were highlighted during the course of this scoping review. The first limitation noted was that literature retrieval from typical bibliographic databases, such as PubMed, was insufficient across all 59 countries for the desired keyword-based information. However, this was circumvented by using a general web-based search engine for keyword identification, which yielded more favourable results. This indicated that the perceived lack of information on the subject matter for SIDS may be partly due to a lack of conversion of reported findings to peer-reviewed publications. Where reports have been submitted to their commissioned institutions and made publicly available, there is minimal formal indexing that would lead to their inclusion in widely used bibliographic databases. Another limitation was the lack of epidemiological studies linking several highlighted challenges with specific health or wellbeing outcomes in SIDS. This lack of attribution can be noted for slow-onset illnesses like chronic non-communicable diseases. However, this uncertainty prevents the definitive establishment of consequences to health due to water insecurity.
In SIDS as a whole, there are four major aspects to consider when discussing water security:
Natural freshwater reservoirs, such as aquifers, streams, rivers, and other water bodies which manifest depending on geology, hydrogeology, and topography. These features are evident in the distribution of natural water resources across SIDS, where 9% have only surface water resources and are typically of volcanic origin, 34% have only groundwater resources which tend to indicate dominance of limestone, and 56% have both ground and surface water resources which indicated more complex geological origins. Targets for preserving natural water resources must focus on proper land use management strategies and maintaining environmental water requirements.
The environmental factors that determine the quantity of water stored naturally such as evapotranspiration, rainfall and other weather extremes controlled by climate zone and aspect. While around 90% of SIDS are located in tropical climate zones which tend to receive significant rainfall year-round or in bimodal seasonal patterns, only 38 of 59 SIDS (64%) utilize rainwater harvesting. Climate change continues to contribute to fluctuations in annual rainfall – as noted by 73% of countries. However, rainwater harvesting should be a more widespread means for supplementing water supply and targets should be placed towards increasing the long-term water storage capacities.
The approach to resource protection which includes waste disposal practices and watershed management. Persistent improper wastewater disposal and treatment has led to contamination of water resources and coastal ecosystems in over 50% of SIDS. Meanwhile, wastewater reuse can offer a solution to the water scarcity plaguing the water-stressed SIDS, while ensuring water resource protection. However, there is a long way to go in implementing management strategies, building capacities for wastewater treatment, and changing negative perceptions towards water reuse in SIDS.
Water supply and distribution infrastructure to ensure even spatial distribution of water throughout a population, despite the geographical concentration of natural or artificial water resources. Over 64% of SIDS have reported having insufficient supply and distribution infrastructure, which includes 5 SIDS categorized as water abundant, and 10 classified as having adequate natural water resources. There is a tendency towards well-distributed pipelines across urban areas, making rural communities particularly vulnerable during dry seasons. Considering that equity of supply is a basic requirement of universal water access, more focus must be placed on improving piped water access, which also facilitates ensuring water quality standards are met. At the same time, non-revenue water (reported by at least 13 SIDS) through water theft or faulty infrastructure worsens the economic burden of providing water and must be eliminated for efficient water management.
Even in middle- to high-income countries where over 90% of the populations have access to piped and treated water, water security remains an uncertainty due to extreme fluctuations in precipitation and delays in the maintenance of supply infrastructure. The uphill battle of meeting water demand in SIDS is being undermined by shifts away from climate precedents. More intensive adaptive measures are required for managing water resources in countries with already stretched resources and extremely limited budgetary allocations for addressing shortfalls in water logistics management. The solutions being explored to combat the challenges hindering water security must approach sustainability from the perspective of technological efficiency as well as local appropriateness.
The burden of water stress on health, therefore, becomes not only an issue of regulating the quantity and quality of water resources but also of a country's ability to reduce the connected health risks. Coming out of this scoping review, it was determined that four of six main challenges (seasonality, inadequate infrastructure, saltwater intrusion, and pollution) require further exploration of the risk factors for the development of infectious diseases, and non-communicable diseases associated with droughts, salinization, and improper waste and wastewater management. This review acts as a seminal piece synthesizing existing literature on the challenges to WRM and is the first such review assessing the intersection between water security, climate change, and health in SIDS. The review will be used to design a multifaceted index that shows the human health burden of water insecurity on SIDS. Visualizing the interconnectivity of issues and solutions will better enable governments and stakeholders to assess target areas based on the highest need and the potential impacts to human health.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.