Waukesha County

Water Well FAQs


  • How can my well become contaminated?

    Your well may become bacteriologically contaminated for one of the following reasons:
    There is a source of contamination too close to the well or the well casing isn’t deep enough to assure that recharge water receives sufficient filtration to remove bacteria. The well may be constructed using poor sanitary practices. New wells often show contamination because during drilling of the well, the drill hole was contaminated through use of dirty tools, pipe and drilling water. New piping, pump or pressure system components also may cause contamination if they are generally soiled and not disinfected prior to use, assembly or installation. The state well code requires disinfections of new wells, pumping equipment and water systems prior to use.

    Contaminated surface water or groundwater enters an improperly constructed well (for example):
    - “Dug” wells that are walled up with boards, brick, stone or tile sections allow unfiltered surface water and near-surface water to seep into the well through the cracks.
    - Casing improperly sealed into the rock and/or unconsolidated geological formation may permit surface water or contaminated groundwater to move vertically downward, contaminating good aquifers.
    - Surface water enters the top of the well because the casing doesn’t extend far enough above the ground or a hand pump base isn’t sealed watertight on the casing.
    - The well top ends in a nonconforming well pit subject to flooding or seepage of contaminated groundwater.
    - Old well casings may rust through, leaving holes near the ground surface where surface water or near-surface waters can seep in and contaminate deeper groundwater.
    - The aquifer supplying the well is fractured rock that has poor water-filtering properties.

  • What do the results of the bacteriological water test tell me?

    Bacteriological examinations are made to determine the suitability of water for drinking and food preparation uses. When a sample is reported “safe bacteriologically,” coliform organisms (a group of indicator bacteria) were not found in the sample. If the sample was taken according to directions enclosed with the water sampling kit, you can be reasonably sure that the water is suitable for drinking and general domestic use. When a sample is reported “unsafe bacteriologically,” coliform bacteria were found in your sample. Coliform bacteria are found in the feces and excreta of humans and other animals as well as in soil and surface water. Their presence in groundwater (wells) shows that unfiltered or poorly filtered surface water or near-surface waters have found their way into the groundwater or entered through an opening in, around or at the top of the well casing. This indicates that the water is potentially dangerous and should not be consumed unless boiled.

  • What should I do if I get an “unsafe sample” result?

    You should:
    1. Resample. A second sample must be taken to confirm your first unsafe result. Be sure to use the proper sampling procedure in taking the sample because it will help you determine if your original unsafe sample was due to human error in sampling.
    2. If the second sample results are unsafe, do not consume the water unless it is boiled at a rolling boil for at least five minutes.
    3. If you can find no obvious sources of well contamination, a qualified person (well driller, pump installer, or owner) should disinfect your water system. To view or download the well chlorination procedure see the link below. Well Chlorination Procedure
    4. If you find obvious sources for well contamination or disinfections is unsuccessful, call our office at (262) 896-8300 to speak to a sanitarian.

Waukesha County Environmental Health
515 W. Moreland Blvd • AC 260
Waukesha WI 53188 (directions)

Hours Monday - Friday • 8 am - 4:30 pm (closed holidays)

Contact us
 | Phone 262-896-8300 | Fax 262-896-8298
Visit us in person in room AC 260