Coliform bacteria are a group of microorganisms that are normally found in the intestinal tract of humans and other warm blooded animals, and in surface water. The presence of these organisms in drinking water suggest contamination from a surface or shallow subsurface source such as cesspool leakage, barnyard runoff or other source. The presence of these bacteria indicate that disease-causing (pathogenic) organisms may enter the drinking water supply in the same manner if preventive action is not taken. Drinking water should be free of Coliform.
Cysts and viruses are microbiological contaminants, usually found in surface water supplies. Giardia lamblia cysts can cause giardiasis, a gastrointestinal disease. Another "bug" getting a lot of attention lately, is cryptosporidium, single-cell parasite measuring about 2 - 5 microns in diameter. Many surface water supplies contain this pest, which also comes from the intestine of warm blooded animals.
Nitrate in drinking water supplies may reduce the oxygen carrying capacity of the blood (cyanosis) if ingested in sufficient amounts by infants under 6 months of age. This could cause a disease called "methemoglobinemia", or "blue baby" syndrome. The EPA has established a maximum contaminant level (MCL) for nitrate at 10 mg/l (ppm) measured as N. Unlike Coliform or other types of bacteria, boiling the water will actually INCREASE the amount of nitrate remaining in the water, increasing the danger to infants. If you have high nitrate water, either treat it with an approved treatment methodology or find another source: Boiling will only make it worse!
Lead is now known to leach from older sweat joints in copper pipe. As the water sits in the pipes, small amounts of lead 'dissolve' into the water, contaminating it. Lead is particularly harmful to small children as they more rapidly absorb the toxic substance into their systems. The EPA has estimated that more than 40 million U.S. residents use water that contains more than the recommended levels.