Drinking water Technology, Eawag, developed a method by which hazard maps could be produced for geogenic toxic substances in groundwater. This provides an efficient way of determining which wells should be tested. Parameters for drinking water quality typically fall within three categories: Physical and chemical parameters include heavy metals, trace organic compounds, total suspended solids (TSS), and turbidity. Microbiological parameters include Coliform bacteria, "E. coli", and specific pathogenic species of bacteria (such as cholera-causing "Vibrio cholerae"), viruses, and protozoan parasites. Chemical parameters tend to pose more of a chronic health risk through buildup of heavy metals although some components like nitrates/nitrites and
Water supply a few days a week. It is estimated that about half of the population of developing countries receives water on an intermittent basis. Drinking water quality has a micro-biological and a physico-chemical dimension. There are thousands of parameters of water quality. In public water supply systems water should, at a minimum, be disinfected—most commonly through the use of chlorination or the use of ultra violet light—or it may need to undergo treatment, especially in the case of surface water. For more details, please see the separate entries on water quality, water treatment and drinking water. Water pressures vary in different