Waterborne diseases are conditions (meaning adverse effects on human health, such as death, disability, illness or disorders)[1]: 47  caused by pathogenic micro-organisms that are transmitted by water.

[3] Lack of clean water supply, sanitation and hygiene (WASH) are major causes for the spread of waterborne diseases in a community.

Therefore, reliable access to clean drinking water and sanitation is the main method to prevent waterborne diseases.

[4] Microorganisms causing diseases that characteristically are waterborne prominently include protozoa and bacteria, many of which are intestinal parasites, or invade the tissues or circulatory system through walls of the digestive tract.

[6] The term waterborne disease is reserved largely for infections that predominantly are transmitted through contact with or consumption of microbially polluted water.

[citation needed] A related term is "water-related disease" which is defined as "any significant or widespread adverse effects on human health, such as death, disability, illness or disorders, caused directly or indirectly by the condition, or changes in the quantity or quality of any water".

[citation needed] Lack of clean water supply, sanitation and hygiene (WASH) are major causes for the spread of waterborne diseases in a community.

[10] Scientists stated a clear observation in 2022: "The occurrence of climate-related food-borne and waterborne diseases has increased (very high confidence).

The World Health Organization estimates that 58% of that burden, or 842,000 deaths per year, is attributable to a lack of safe drinking water supply, sanitation and hygiene (summarized as WASH).

"[24][25] WBDOSS relies on complete and accurate data from public health departments in individual states, territories, and other U.S. jurisdictions regarding waterborne disease and outbreak activity.