**10. Which Water-Related Pathogens Are Important?**

A wide range of pathogens are known to be transmitted through water (Table A1, Appendix A). Historically, some diseases, such as cholera, dysentery and typhoid have been very important from a public health perspective, causing extensive morbidity and mortality. Many of the diseases are a problem where there is limited infrastructure, as in developing countries or rural regions of developed countries and can be sensitive to social disruption and infrastructure damage. It is important to understand the future health impacts of climate change and to understand where the most important disease burdens will be. Waterborne diseases can be sensitive to emergence, but this is generally related to the discovery of new infectious agents or identification methods (e.g., cryptosporidiosis, microsporidiosis, legionellosis, hepatitis E) rather than newly emergent diseases. However, some classical waterborne pathogens may emerge in new areas with climate change (e.g., cholera), and Legionnaires' disease, which is predominately derived from contaminated water systems in the built environment, may increase as a result of raised temperatures.

An examination of 24 analytical studies assessing the association between extreme precipitation or temperature and drinking water-related waterborne infections, found that most studies showed a positive association with increased precipitation or temperature. A few studies showed an association with decreased precipitation and several in which there was no association [117]. Infections included cholera, typhoid, paratyphoid, campylobacter, shigella, hepatitis A, cryptosporidiosis, giardiasis and waterborne outbreaks.
