Is my water safe to drink?

It is not uncommon in some parts of the country for lakeshore residents to use their local lake as a drinking water source. Although any public health official will tell you not to drink untreated surface water, there are still many that do. Surface water can be contaminated by coliform bacteria, bluegreen bacteria, Giardia, Cryptosporidia, and other pathogens. So how do you know if your water is fit to drink?

Drinking water supplies should be tested regularly. The most common test for drinking water is bacteriological -- a measurement of the numbers of bacteria within a certain volume of water. The coliform group of bacteria is the principal indicator of suitability of a water for domestic use.

About Coliform Bacteria

Coliform bacteria can be numerous in the natural environment, occurring naturally in soil, water, and the intestines of animals. Total coliform is a measure of all coliform bacteria. Fecal coliform and fecal streptococcus bacteria are indicators of fecal pollution from warm-blooded animals. Sources of fecal coliform bacteria may be natural (beaver, deer, water fowl) or cultural (septic systems, livestock).

Drinking Water Standards

The U.S. EPA has established that the maximum number of total coliform organisms in drinking water supplies (wells or treated surface water) is 1 colony per 100 milliliters (mL). There are no specific standards established for lake water used for consumption by individuals. Treated drinking water (filtered or chlorinated) from shallow wells and surface waters should be tested for total coliforms to determine compliance with EPA Drinking Water Standards. However, since it is fairly common to detect some total coliforms in shallow ground water (hand-dug wells or well points) and lake water, it is more appropriate to selectively test for fecal coliforms for those who drink water from those sources without treatment.

Understanding Coliform Results

Coliform results are expressed as the number of colonies per 100 mL of sample. Total coliform counts in deep well or treated water of less than 1 colony per 100 mL pass EPA Drinking Water Standards and are considered safe to drink. In untreated surface waters, total coliform counts above 1 colony per 100 mL are possible and do not necessarily indicate a health hazard. Fecal coliform counts should also be less than 1 colony per 100 mL in treated and untreated drinking water. Fecal coliform results greater than 1 colony per 100 mL indicate the potential for pollution by sewage, although the source could also be from wildlife. A second test is recommended in those cases.

Limitations of Bacteria Testing

There are several problems with bacteriological testing of lake water to determine suitability for drinking. Since surface water is an uncontrolled source, constantly flowing and exposed to all sorts of potential contamination, an acceptable result from one sample does not guarantee that the next drink of water will be pure. Furthermore, it is extremely important to note that the fecal coliform test does NOT detect contamination by Giardia, Cryptosporidia, or other pathogens. Since these organisms are widespread in the environment, can cause protracted illness, and are difficult to measure, the only safe bet is to treat the water.



Safe Drinking Water
 

There are several alternatives for insuring a safe drinking water supply if you use lake water. One is to boil all water that you drink or use for cooking. Another is to install a filter with a pore size of 0.4 microns and use that water for drinking and cooking. It is not essential to filter all water, such as for showers or flushing. Installation of a pre-filter for sediment removal will prolong the life of the drinking water filter. If your lake experiences blooms of bluegreen bacteria (a type of algae), you should also use a carbon filter to remove any organic contaminants since several species of bluegreen bacteria produce hepatotoxins which can cause liver damage after prolonged exposure.

F. X. Browne, Inc., 800-220-2022, info@fxbrowne.com
Your State or County Health Department