contaminants in the water come from human or animal waste; if ingested, they can cause gastroenteric diseases, or intestinal disorders. Public water supplies are therefore treated to eliminate these microorganisms. In the past, coliform bacteria tests were used to determine how effective the treatments were: If no coliform bacteria was found, the water was believed to be devoid of all harmful organisms. However, that's not necessarily true. The disinfection used to kill coliform bacteria may not affect tougher organisms like cryptosporidium and giardia (Jar DEE uh). In addition, viruses can often 'slip through' the filtration system, as they're much tinier than the bacteria and sediment that's normally removed. Viruses can also be somewhat resistant to disinfection. Currently, the EPA is considering recommendations to lower the amount of particles allowed in water supplies. The problem is, few devices can measure such minute differences in water clarity. New instruments called 'particle counters' look promising; but they're also relatively expensive, and not in widespread use. This issue is being explored by the EPA, as the agency seeks to find ever more effective ways to remove microorganisms from the public water supply.
