Drinking Water Well Basics

What is an onsite water supply system (well)?

In areas where public water supply is not available, homeowners must install a well to pump groundwater to their home home. Washtenaw County homeowners should feel confident that safe, adequate water will be obtained on their property. However, there are some areas in the County where water quality and quantity can be an issue. For more information on these areas, contact Environmental Health at (734) 222-3800.


What are typical water supply system components?

Well Photo Courtesy of Dupage County

  • Casing:  The casing is a tube in the ground that houses the well pump and the pipe that moves water from the pump to the surface. It also prevents the hole from collapsing, and keeps contaminants from entering the water supply. Modern well casings are typically 5" plastic (PVC) pipe.
  • Cap:  The cap is the top of the well casing. The cap must end at least one foot above ground so it is not subject to flooding. The cap usually has a screened vent to prevent insects from entering the well.
  • Pump:  The well pump draws water up the hole and pushes it into the home. The well pump is usually submersible. This means the pump is installed in the well casing several feet below ground, making it operate more quietly.
  • Pressure Tank:  The pressure tank is usually a 3-4 tall cylinder located in the home. It stores water and distributes it through the home at an even pressure. The tank can also serve as additional storage for low-yield wells. The pressure switch located at the tank controls the pumps on/off cycle.
  • Pitless Adapter:  The pitless adapter is a plumbing fitting that attaches to the well casing and routes the water supply line from the pump to the home. It is installed approximately 4 below ground so it is not subject to freezing. Before these were invented, old wells often terminated below ground in pits, or basement off-sets. Pits are no longer necessary, hence the name pitless adapter.
  • Screen:  The screen is at the very bottom of the well, attached to the casing. It keeps sand and gravel out of the well while allowing groundwater to flow into the well. Some wells drilled into bedrock do not need screens since the water travels through crevices in the rock, and there is no sand to filter out.


What tests do new wells need?

Once the well is installed, the water must be tested to show it is safe. Sample bottles are available from Environmental Health. New wells must be tested for:

  • Bacteria: Must be negative.
  • Arsenic: Must be 10 parts per billion (ppb) or less.
  • Nitrates: Must be 10 parts per million (ppm) or less.


Does my well need any maintenance?

Most wells have a long service life of over 20 years. Follow these tips to ensure a safe supply of drinking water:

  • Keep household chemicals, paint and motor oil away from your well and dispose of them properly by taking them to a recycling center or household hazardous waste collection site.
  • Limit your use of pesticides and fertilizers.
  • Keep your well cap clear of leaves, mulch, dirt, snow and other materials.
  • Use caution when mowing around your well so you don't damage the well casing.
  • Practice water conservation in your home and install low-water-use appliances.
  • Keep your well records (such as the well construction report, water test results, and maintenance records) in a safe place.
  • Test your water yearly for bacteria (E. Coli)!


For more information, please contact:

  • Your Area Sanitarian (based on your Township)
  • Washtenaw County Environmental Health Division - (734) 222-3800
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