Diseases related to contamination of drinking water constitute a major burden on human health. The great majority of water-related health problems are the result of microbial (bacteriological, viral, protozoan or other biological) contamination. Sanitary surveying of drinking water is an important tool for reducing the risks of water contamination and waterborne illness. In Study Session 15 you learned that undertaking a sanitary survey is an important part of the process to develop a new water source. Sanitary surveys are also essential for monitoring the condition of existing water sources to ensure they continue to be safe to use.