**3. Climate Change and Drinking Water-Related Infectious Diseases**

The history of water-related disease dates back to the classical period when Empedocles is reported to have introduced drainage of a swamp (a public health intervention) to reduce disease [23]. The ability of waterborne diseases to cause large outbreaks that, in the case of typhoid and cholera, have a high morbidity and mortality, makes them important historically. A classification of water-related infections was drawn up by Bradley (Bradley's classification [24]) and has been adapted by others [25–27]. A modified-version groups diseases into waterborne; water access related; water based; water-related insect vectors; and engineered water systems, although this revision still excludes some water-related diseases (Table 1).

Drinking water is the most important waterborne disease risk because the contamination of large mains supplies can cause large outbreaks [28–32], and because small rural supplies are commonly contaminated [33,34] which, in developing countries, can lead to substantial infant mortality. Bottled water is usually safe, particularly natural mineral waters that are derived from deep wells or other secure sources, but outbreaks may occasionally occur. The water supplies on ships, trains and aircraft can be subject to contamination where the supply chain breaks down [35]. There are always potential risks when people drink untreated natural waters. The supply of clean water can become critical in areas of war, disaster, famine, drought, water shortage and flooding, and refugee supplies often need to be established rapidly to prevent outbreaks [36–41].

While climate change may affect the microbiological quality of water and water-related diseases, the arguments indicate notable uncertainty over what the specific impacts will be, and when and where they will be most acute. However, to assess the likely impacts upon the health of humans, there is a need to examine the resilience of society to changing water quality. Developing an understanding of these capabilities and adaptation potentials is key to assessing the likely influence of climate change.


**Table 1.** Criteria for water-related diseases [24–26,42].

One of the major pathways through which contaminated water affects individuals is though drinking water. In terms of management, these supplies range from unimproved sources where the individual is effectively consuming raw water, to large, managed supplies where multiple barriers exist to prevent microbiological contamination of water supplies. Climate change has a number of potential influences upon water treatment, and higher temperatures are known to enhance biological methods of water treatment [43]. However, countering this effect are a number of other factors linked to more extreme weather, such as increased rainfall and water turbidity [44,45] which may increase risks to microbiological water quality in some locations. A review of the impacts of climate change on surface water contamination concluded that it was likely to increase the risk associated with drinking water supplied mainly during extreme climatic events [46]. Pathogen risk was argued to rise mainly due to elevated temperatures and extreme rainfall, especially in temperate countries.

Ensuring appropriate water infrastructure, regular monitoring and appropriate management techniques, such as Water Safety Plans, are likely to be increasingly important to address changing risks. In the future rapid testing (e.g., PCR based) [47] and new treatment technologies (e.g., nanomaterials) [48] may play an increasing role in addressing climate change challenges. The ability to respond to changing risks will vary according to the resources available. In terms of supplies less able to adapt to a changing water quality, we highlight small water supplies, private water supplies as well as supplies in lower income areas as potentially being at greatest risk.
