**9. Climate Impacts on Water, Sanitation and Hygiene (WASH)**

Understanding the climate change impacts on water-related diseases requires an understanding of water, sanitation and hygiene. Much of the burden of waterborne disease appears to result from small and rural supplies, although there may be under-ascertainment of outbreaks in urban areas with mains supplies due to limited disease surveillance. This is important in an examination of the burden of waterborne disease and future changes as a result of altered weather patterns. Waterborne disease burden methodologies used in developed countries to attribute acute gastrointestinal infection (AGI) to drinking water, include simple point estimates, quantitative microbial risk assessment, Monte Carlo simulations based on assumptions and epidemiological data from the literature [94]. In developing countries, inadequate water and sanitation are associated with risk of diarrhoeal disease [95], particularly in young children, and raised maternal mortality occurs in households with poor sanitation and a poor water environment [96]. The microbiological quality of household water correlates with health outcomes (diarrhoea and trachoma) [97], although improved sources do not always provide water that is completely free of faecal contamination. Point of use devices can be effective [98], however, contamination of water between source and point of use remains a continuing problem [99]. An examination of interventions to reduce diarrhoea in less developed countries found, that while interventions were generally effective, the heterogeneity between studies made the exact conditions causing disease reductions difficult to assess [100], and others found a dearth of methodologically sound studies [101]. There were also inadequacies in behavioural models and frameworks for intervening in WASH specific interventions [102]. The impacts of WASH on child diarrhoeal morbidity has been examined in a number of studies [103] and there was a general lack of good quality studies of diarrhoea morbidity in children in India [104]. While water treatment (e.g., chlorine water treatment at point of use) can be effective, most studies are short term [105]. An examination of water distribution system deficiencies demonstrated that study blinding can be important [106]. Expecting to obtain good information on the risks from water-related infections under climate change, in the absence of reliable, experimental evidence for effectiveness of interventions, seems naïve.

Of 293 outbreaks linked to water supplies in Canada and the US, failure of existing treatment and lack of water treatment were the leading causes [107]. Temporary water outages and chronic outages in intermittently operated systems can be associated with gastrointestinal infection [106]. The Walkerton outbreak of *E. coli* O157 and *Campylobacter* in Canada highlighted the role that heavy rainfall can play in outbreaks [108,109]. However, this was also linked to poor management. There are many studies that have examined the role of rainfall before an outbreak. It is generally seen that heavy rain is more common before many outbreaks, suggesting the source water is compromised [32,36,110–112]. The association between waterborne outbreaks with a period of prolonged low rainfall in the four weeks before an outbreak may also indicate a vulnerability to weather [32], although this was not seen in other studies. There is a strong need for water utilities to build water safety plans that factor in likely changes in climate over future scenarios, while retaining an understanding of historical weather events. Behaviour change interventions for water and sanitation in developing countries have looked at risk factors, attitudinal factors, normative factors, ability factors, and self-regulation factors [113]. Social marketing for water and sanitation products showed this improves health threat awareness and provides a solution to reducing disease burden [114]. Good water sourcing, treatment, distribution, storage and clean point of use remain the key to community health. Water and sanitation in schools is an important area where improvements can facilitate improved educational achievement [115].

There is a need for robust epidemiological studies that quantify the health risks associated with both small, private water systems, and large community supplies. More information is needed on pathogen quantification, susceptibility of vulnerable sub-populations, the influence of extreme weather events, the proportions of the population served by different water sources and the treatment level, source water quality and condition of the distribution system infrastructure. The exposure to faecal contamination in potable water has been estimated, suggesting that there may be a substantial under-estimate of disease burden [116].
