Elisa Shackelton: Have you tested your well-water?

Quick facts

• Bacterial contamination of drinking water can cause serious human illness.

• Bacterial slimes in irrigation wells may clog pumps and pipes.

• Bacterial contamination can be controlled by well chlorination, proper septic system and well maintenance, and good sanitation practices.

— Public drinking water supplies are required, by law, to be free from microbial pathogens.

However, private water systems, while also vulnerable to contamination from bacteria, usually have no governmental oversight.

If you rely on a private well, it is your responsibility to ensure the water is safe to drink.

You should inspect the condition of your well regularly and test a water sample every one to two years. More frequent testing is recommended when well condition is poor, the well has been inundated with floodwater, the septic system has malfunctioned, abandoned wells or feed yards are located nearby, or visitors have complained of stomach or intestinal distress.

Bacteria in your water may indicate that your well has become contaminated with fecal matter, possibly introducing harmful viruses and protozoa such as Cryptosporidium or Giardia.

It is important to periodically inspect exposed parts of the well for problems such as:

• A cracked, corroded or damaged well casing

• A broken or missing well cap

• Settling and cracking of surface seals

Collecting samples

It is best to collect a water sample at a bathroom faucet with the aerator removed. If you are retesting a well that has previously tested positive for bacteria or after a disinfection treatment, sample as close to the well as possible. If you have a holding tank or in-house water treatment system, you may want to collect separate samples at the well and at the bathroom faucet. Kitchen faucets with swivel arms are not recommended locations for sampling. Before filling the sample bottle, run cold water though the faucet at full flow for three minutes, and then reduce the flow to a trickle and let run for one additional minute. Wash your hands with soap and warm water before opening the sterile sample bottle (do not touch the inside of the bottle or lid). Do not rinse the sample bottle before filling to the level indicated on the bottle. Cap the bottle tightly and label it with your name, address, date and time of sampling. Keep the sample cool and deliver it to the lab within 24 hours.

Interpreting lab results

There are a variety of bacteria, parasites and viruses that cause health problems when humans ingest them in drinking water. Testing water for each of these germs is difficult and expensive. Instead, water quality and public health workers measure coliform levels. The presence of coliforms in drinking water suggests there may be disease-causing agents in the water. Coliforms are a broad class of bacteria that live in the digestive tracts of humans and many animals. Labs may test for total coliforms, fecal coliforms or E. coli, any of which indicate microbial contamination. Results are generally reported as no coliforms present, the actual number of organisms detected per 100 ml of water, or as too numerous to count. Some labs may simply report results as bacteriologically safe or unsafe. If your drinking water contains more than 1 coliform organism per 100 ml or is reported as unsafe bacteriologically, the well should be disinfected and retested in one to two weeks. If subsequent tests indicate bacteria are still present, the source of the contamination must be identified and eliminated before the water is safe to drink.

Disinfecting wells

There are several options for private water supply disinfection. These include continuous chlorination, shock chlorination, ultraviolet radiation (UV), ozonation, boiling and pasteurization. Each of these methods has advantages and limitations, but they are all intended for use on clean, clear water. Water supplies must be sealed and protected from sources of bacterial contamination for disinfection methods to function properly.

For water testing bottles and/or more information on wells, contact your local Colorado State University Extension County office. The CSU Extension publication #6.703, "Bacteria in Water Wells," along with other CSU water quality publications, is available online at http://www.ext.colostate.edu/pubs/natres/06703.html.


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