This often occurs in the Pacific Northwest in late winter, when flooding inundates wells and septic systems, mixing drinking water with contaminated water. The most common method used to determine if water supplies are contaminated is a coliform test. Coliforms, or bacteria that live in the intestines of humans and animals, are not necessarily hazardous by themselves, but the presence of coliforms indicates that hazardous microorganisms might also be in the water. These microorganisms can cause what physicians call enteric diseases, which infect the cells of the intestinal lining, either growing on them or in them. The resulting diseases can be serious, and occasionally fatal.
Symptoms can include cramping, diarrhea, vomiting, nausea and sometimes fever.
People most susceptible to the harmful effects of microorganisms in water are the very young, very old and those individuals with compromised immune systems. In the last several years, microorganisms have contaminated city water supplies in several locations around the country. In Milwaukee in 1993, contamination of the municipal water supply with Cryptosporidium killed some 70 people and sickened more than 400,000. Disease-causing protozoa can sometimes be found in water in rural or developing areas, according to Wyatt. Proper well development and sanitary water storage and transport systems in those regions are the key to water safety.