Table 3

Links between water supply system alternatives and climate change risks in the Pacific (adapted from Howard et al. 2010)

InfrastructureKey threats (globally)Pacific context
Boreholes Drying and salinisation may be issues, but boreholes have high adaptability. Remote outer islands are difficult to access with drill equipment. There is a difference between community and household boreholes, with the former more likely to be deeper and provide more reliable supply during periods of drought (Chan et al. 2020). 
Dug wells Microbial pollution and year-round availability already a problem. Increased drying and salinisation with limited adaptation options. Salinisation due to overtopping events on atoll islands. High permeability and shallow groundwater tables mean atolls are at high risk of contamination from landfill, sewage and agriculture (Werner et al. 2017). 
Protected springs Reduced flow in drying environments or in dry seasons Spring water is used by over 20% of households for drinking water in some communities in Solomon Islands (Elliott et al. 2017), with increasing importance in the dry season when tanks are used less. 
Household rainwater harvesting Increasing variability and intensity of rainfall may not provide year-round supply. Tanks may not be big enough to provide all water needs (McNamara et al. 2020). There is a gap in understanding how water use needs are prioritised at such times (MacDonald et al. 2017). 
Gravity-fed river systems Not discussed Catchments in the Pacific tend to be relatively small and rainfall seasonal, so river-based systems are already not appropriate in some locations. Many islands do not have permanent surface water resources. However, in some locations, e.g. Solomon Islands, up to 90% of households use river water, although relatively rarely for consumptive use (6–11%) (Elliott et al. 2017). 
Treatment processes Processes are resilient but climate change may increase treatment requirements Remote and distributed geography increases cost and potential for maintenance delays, particularly following extreme events/disasters. Maintenance can be affected by lack of resources in water authorities. Back-up rainwater tanks are suggested as one alternative for mitigating such risks (MacDonald et al. 2017). 
Piped water Damage to systems can impact large populations. Highly complex systems, with options for more robust design and operation – depends on management and the financial position of the water authority. May be strongly groundwater dependent in some parts of the Pacific so sustainability of use and impacts of climate change on recharge need to be considered (Carrard et al. 2019). 
Alternative sources Not discussed Population densities unlikely to be high enough for desalination to be cost efficient. Access to parts and maintenance needs to be considered (cost and availability). Although not specific to alternative water sources, examples of poor project outcomes due to parts not being easily available are described in McNamara et al. (2020). Bottled water is used by 3–6% of households (Elliott et al. 2017). Some households in outer regions of the Republic of the Marshall Islands report cooking with seawater (Elliott et al. 2017). 
InfrastructureKey threats (globally)Pacific context
Boreholes Drying and salinisation may be issues, but boreholes have high adaptability. Remote outer islands are difficult to access with drill equipment. There is a difference between community and household boreholes, with the former more likely to be deeper and provide more reliable supply during periods of drought (Chan et al. 2020). 
Dug wells Microbial pollution and year-round availability already a problem. Increased drying and salinisation with limited adaptation options. Salinisation due to overtopping events on atoll islands. High permeability and shallow groundwater tables mean atolls are at high risk of contamination from landfill, sewage and agriculture (Werner et al. 2017). 
Protected springs Reduced flow in drying environments or in dry seasons Spring water is used by over 20% of households for drinking water in some communities in Solomon Islands (Elliott et al. 2017), with increasing importance in the dry season when tanks are used less. 
Household rainwater harvesting Increasing variability and intensity of rainfall may not provide year-round supply. Tanks may not be big enough to provide all water needs (McNamara et al. 2020). There is a gap in understanding how water use needs are prioritised at such times (MacDonald et al. 2017). 
Gravity-fed river systems Not discussed Catchments in the Pacific tend to be relatively small and rainfall seasonal, so river-based systems are already not appropriate in some locations. Many islands do not have permanent surface water resources. However, in some locations, e.g. Solomon Islands, up to 90% of households use river water, although relatively rarely for consumptive use (6–11%) (Elliott et al. 2017). 
Treatment processes Processes are resilient but climate change may increase treatment requirements Remote and distributed geography increases cost and potential for maintenance delays, particularly following extreme events/disasters. Maintenance can be affected by lack of resources in water authorities. Back-up rainwater tanks are suggested as one alternative for mitigating such risks (MacDonald et al. 2017). 
Piped water Damage to systems can impact large populations. Highly complex systems, with options for more robust design and operation – depends on management and the financial position of the water authority. May be strongly groundwater dependent in some parts of the Pacific so sustainability of use and impacts of climate change on recharge need to be considered (Carrard et al. 2019). 
Alternative sources Not discussed Population densities unlikely to be high enough for desalination to be cost efficient. Access to parts and maintenance needs to be considered (cost and availability). Although not specific to alternative water sources, examples of poor project outcomes due to parts not being easily available are described in McNamara et al. (2020). Bottled water is used by 3–6% of households (Elliott et al. 2017). Some households in outer regions of the Republic of the Marshall Islands report cooking with seawater (Elliott et al. 2017). 
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