PULLMAN, Wash. — Each year, communities throughout the U.S. face
short-term water quality problems when microorganisms make their way into
public and private water supplies at levels that can cause disease. Often this
occurs in the Pacific Northwest in late winter when flooding inundates wells
and septic systems, mixing drinking water with contaminated water.
Carol Wyatt, a microbiologist and assistant professor in the Department of
Veterinary Microbiology and Pathology at Washington State University’s
College of Veterinary Medicine, studies water-borne, disease-causing
organisms and offers advice on testing, pathogens and water quality
The most common method used to determine if water supplies are
contaminated is a coliform test. Coliforms are bacteria that live in the intestines
of humans and animals. These beneficial bacteria aid digestion by helping
break down food and are excreted in feces.
Specially stained and under a microscope, coliforms are easy to identify in
water samples. High concentrations in a water sample mean the water is
contaminated with feces.
Coliforms themselves aren’t necessarily hazardous, but the presence of
coliforms indicates that other hazardous microorganisms might be in the water.
These microorganisms can cause what physicians call enteric diseases.
Enteric disease microorganisms 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.
Enteric disease microorganisms can be in the form of bacteria, viruses or
protozoa. Two types of protozoa, Giardia lamblia, known for causing
“backpacker’s diarrhea,” and Cryptosporidium parvum, a common cause of
“traveler’s diarrhea,” are of particular concern.
In the last several years these agents have contaminated city water supplies in
several locations around the country. In 1993, Cryptosporidium contamination
of the Milwaukee municipal water supply sickened more than 400,000 and killed
some 70 people.
People killed by microorganisms in water are usually the very young, the very
old, and those individuals with insufficient immune systems.
Disease-causing protozoa can sometimes be found in water in rural or
developing areas. Generally, wild animal feces containing the protozoa
contaminate the water supply. Proper well development and sanitary water
storage and transport systems in those regions are the key to safety.
Protozoa can be difficult to eliminate from water supplies. They resist
commonly prescribed antibiotics, as well as chlorination.
Filtration is one way to remove some contaminants from water, and several
water filtration systems are available for home use. But no filter system is
Physical filters are made of fibers, ceramics or fabric. Activated carbon filters
often include silver, a toxic element to some microorganisms. Reverse osmosis
filters pass water through membranes and collect it in storage tanks. Ultraviolet
disinfection units pass water through a beam of ultraviolet light.
Ozone, a naturally occurring form of combined oxygen molecules that destroys
certain microorganisms, has been used to treat water but is also expensive.
Sometimes, different systems are combined to treat water in small quantities.
Cities don’t use filtration because it’s usually too expensive and can’t
decontaminate large quantities of water fast enough.
Municipal water is regularly tested for a variety of pathogens and chemicals
and must meet EPA standards under the Safe Drinking Water Act.
Homeowners are notified if drinking water becomes unsafe and contamination
sources are then located and eliminated.
Even today, with many advances in technology, the best way of killing
microorganisms in water is to boil it hard for 20 minutes. Boiling is the most
common advice water managers give when they are faced with major water