The future of water and sanitation: global challenges and the need for greater ambition

Water and sanitation services are critical for public health. The importance of these services is reflected in SDG 6 and the associated targets 6.1, 6.2 and 6.3. Much progress remains to be made to achieve these targets, but it is already becoming clear that greater ambition is needed. This paper looks at three global challenges: the need to increase the level of service to protect public health including infectious respiratory diseases; the role of sanitation in combatting anti-microbial resistance (AMR); and the urgent need to build more climate-resilient services. We need to upgrade the SDG targets to focus on universal access to piped water on premises, to incorporate action on AMR in definitions of safe sanitation and to embed actions to improve resilience, which take into account the greater ambition called for in the SDG 6 targets. This requires a shift in thinking in the sector, away from relying on households and communities to manage their services to properly funded, professional services staffed by trained technical, managerial and finance staff. This will require more public finance and better use of financial instruments that have proved effective in other sectors. Increasing our ambition will mean the world can achieve the aim of universal access to safe, sustainable, and resilient services and protect public health.


INTRODUCTION
Water and sanitation services are critical to protecting public health. They are also recognised human rights under international law (UNGA ). Ensuring effective delivery of these services is one of the most basic responsibilities of any government leading to social and economic benefits to the population of their countries. However, as the international monitoring data in Table 1 shows, the world has a long way to go to ensure everyone gets access to safe services.
These data mask huge inequalities between regions, with regions with more low-and middle-income countries (LMICs) typically having much lower rates of access. The Joint Monitoring Program (JMP) reports demonstrate persistent inequalities in access to water and sanitation between rural and urban areas and between the richest and poorest population quintiles (UNICEF & WHO ). Even in high-income countries, the levels of safety and regulation afforded to small, rural water supplies are substantially lower than those associated with larger utility water supplies. In wealthy countries such as the USA, there remain communities that lack running water, sanitary toilets or face significant contamination threats and substantial numbers of homeless people who lack sustained access to safe water and sanitation (Riggs et al. ; Capone et al. ).

GLOBAL TARGETS
The importance of water and sanitation is reflected in the Sustainable Development Goals (SDGs). SDG 6 aims to 'Ensure availability and sustainable management of water and sanitation for all' by 2030 (UNGA ). There are six targets under SDG 6 aimed at measurable improvements in water and sanitation and two further targets focused on how these targets should be achieved (see Box 1).
The three first targets of SDG 6 relate to the delivery of drinking water supply and sanitation services and the management of wastewater quality. There are numerous challenges in achieving global objectives for water and sanitation including urbanisation, economic growth and recession, and environmental change and pollution. However, this paper focuses on three of the most significant challenges which required concert global action: ensuring drinking water supplies are safe and support effective hygiene; the role of sanitation in combatting the spread of anti-microbial resistance (AMR); and climate change.

INCREASING LEVELS OF SERVICE TO ACHIEVE PUBLIC HEALTH BENEFITS
The underlying rationale for the provision of water and sanitation services and treating wastewater is the protection of public health (Bartram & Cairncross ). Our understanding of the threats has deepened and widened since John Snow's ground-breaking action in the 1850s. It has been understood that the quantity of water is as important as its quality (Waddington et al. ); that levels of sanitation supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity.
6.5: By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.
6.a: By 2030, expand international cooperation and capacity-building support to developing countries in water-and sanitation-related activities and programmes, including water harvesting, desalination, water efficiency, wastewater treatment, recycling and reuse technologies.
6.b: Support and strengthen the participation of local communities in improving water and sanitation management.

ANTI-MICROBIAL RESISTANCE
The If we are to manage the threats of infectious disease, reduce the spread of AMR and ensure resilient sanitation, sanitation services need to be transformed. This does not mean a rush to invest in expensive conventional sewerage systems as in many cases this would represent maladaptation to climate change given the heavy demands for water and energy. On-site systems linked with effective measures to collect, transport, treat and reuse sludge can offer the same levels of safety and will often be more sustainable and resilient than sewerage systems (Howard et al. ).
Organising such services, however, requires better-trained staff, effective regulations and adequate infrastructure.

CLIMATE CHANGE: THE URGENT NEED FOR RESILIENCE
The changes in climate already seen and projected into the future will have a major effect on water and sanitation ser- Increases in ambient temperatures combined with the expansion of piped water systems may increase exposure to opportunistic pathogens than grow within biofilm in engineered systems (Bartram & Hunter ).
Adapting water and sanitation services to ensure that they become more resilient to future climate change will be a defining challenge for the sector over the coming decades. As adaptation is planned, this must consider how a shift to a target of universal access to piped water on premises and sanitation systems that help reduce the spread of AMR may impact on resilience.
Adaptations will involve actions on technology, management, policy and finance (Howard et al. ). In many parts of the world, extreme event occurrences will be likely to

).
Small systems are of special concern in relation to cli- In addition to improved management, other investments will be required to adapt to climate threats, including investment in upgraded infrastructure, improved environmental

CONCLUSION
This paper has focused on three critical challenges facing the water and sanitation sectorits ability to contribute to halting transmission of infectious disease, the increasing threat of AMR and tackling the climate emergency. While other challenges undoubtedly exist, these issues have a global impact and will define water and sanitation for years to come.
These challenges overlap and interact with each other.
Investments to improve access to piped water will mean more return flows into sanitation systems and it will be important to assess what impact this may have on treatment systems designed to reduce the spread of AMR. Investments in sanitation systems to reduce the release of anti-microbialresistant organisms into the environment should lead to reduced contamination of water sources and help improve the safety of drinking water. Investments to improve drinking water and sanitation systems must consider the likely impact of climate change and measures put in place that will enhance resilience.
The global community needs to be more ambitious in its goals for water and sanitation. Shifting to targets of universal access to continuous, safe water on premises that is resilient to future climate change and enhancing the definition of safe sanitation and wastewater quality by including actions on AMR imply substantial shifts in policy, practice and finance. While the temptation may be strong to resist increasing our ambition given current rates of progress appear to be so slow, failing to do so will mean remaining vulnerable to outbreaks of disease, continuing to consign people to poverty and limiting their economic opportunities, and increasing vulnerability to the effects of climate change.
These challenges can be met but require the sector to reassess how such essential basic services can be effectively delivered. Technology development and innovation will remain an important strand in this, but the key will be the professionalisation of services and a move away from the delegation of responsibility to communities and households.
There needs to be more effective use of existing finance and expanded public investment in these services and using financial instruments from other sectors that have proved effective should be explored. Further research is required on key aspects, such as combatting AMR and improving resilience, but this should not hold back actions that can be taken now.
Ultimately, to protect public health and help reduce poverty, the world needs to increase its ambition of water and sanitation. Redefining SDG targets is an important first step and would demonstrate a long-term commitment to delivering the basic services all humanity needs.

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.