Private well water and your health

What is private well water?

Private and individual household wells are those that serve fewer than 25 people and are not regulated by the Safe Drinking Water Act. Typically, private wells supply drinking water to one home and are maintained by a private owner. In Colorado, about 15% of residents get their drinking water from a private well.

Why is well water a concern?

Private well owners are solely responsible for the quality of their drinking water. So it is up to you, the well owner, to decide when and how to test the water quality of the water from your well. Without testing, the water quality is unknown and the water could be contaminated with natural-occurring or other contaminants. Private well water may contain some natural impurities or contaminants, even with no human activity or pollution. Health concerns vary for different people and depend on amount of contaminants in water, as well as frequency of contact and/or you have been drinking the water.
Unlike a public drinking water system, private wells do not have experts regularly checking the water quality before it is sent to the tap. Private well water quality varies from source to source depending upon:
  • the well’s depth below surface
  • the aquifer and geologic formation it is in
  • surrounding land use(s)
  • well integrity

What is known about well water quality and human health?

The presence of contaminants in private well water is not necessarily a health risk. It is reasonable to expect all water will have small amounts of some contaminants in it. Even having drinking water that has levels of contaminants above drinking water standards set by U.S. Environmental Protection Agency (EPA) does not necessarily mean that you will become ill. Some contaminants, such as bacteria or nitrate, can result in illness quickly after a short or small exposure, other contaminants create a health concern after long exposure, for example after years of exposure to levels above EPA health standards.
The health effects of any contaminant depend on:
  • How much is in the water
  • How a person is exposed to it (for example, through drinking or showering)
  • How often and how long a person is exposed to the contaminated water
  • If that person is particularly vulnerable (for example, children or someone who already has a health problem)

Some of the possible health effects of contaminated water include:

  • Gastrointestinal illness: Nausea, vomiting and diarrhea can be caused by microorganisms in drinking water. Illness can begin soon after the person is exposed to the contaminated water
  • Cancer: Some contaminants in drinking water, such as metals and solvents, can increase a person’s risk of getting cancer if the person is exposed to the contaminant over many years
  • Some contaminants can increase the risk of conditions such as kidney disease, cardiovascular effects, or neurologic or developmental disorders
  • Some contaminants can increase the risk of conditions like blue baby syndrome (methemoglobinemia), skin rash, or lung irritation
Several health effects have been associated with exposure to contaminants in drinking water in scientific studies. Some chemicals have been studied for many years and their effects on health are well understood. Others need more research to help us understand these connections better and see if these results are confirmed by additional studies. 

Who is at risk?

People who own private wells are responsible for sampling them to make sure the water is safe to drink. Private well owners should test their water annually, and in some cases more often. More frequent testing may be needed if:
  • someone in the household is pregnant or nursing
  • there are unexplained gastrointestinal illnesses in the household
  • contaminants are found in a neighboring well
  • there is a change in water taste, odor, color or clarity
  • there is a spill of chemicals or fuels into or near the well
  • there has been a recent natural disaster such as a flood or fire
What should I know about testing my well?
How often you test your well and what tests should be done will depend on many factors such as where you live, local geology, and what activities take place near the source of your well water. You can find out more about what is currently known about private well water quality in Colorado by going to the ‘Maps’ tab under that data query section or expand the Private Wells in Colorado map module on this page. You can also find out more about private well water quality on the USGS website

CDPHE has additional information about when to test your well and how to interpret your test results in these fact sheets:

You can learn more about how and when to test your well water by going to these links:

You can learn more about how and when to test your well water by going to these links:

How can risk be reduced?

Well owners should always use a licensed contractor to construct water wells, install pumping equipment, and for any major repair or maintenance.
Private well owners should educate themselves, by contacting their local health department for information on getting their water tested. Local health departments may also provide some insight on the placement and construction of new wells meeting state and local regulations. Most have rules about locating drinking water wells minimum distances from septic tanks, drain fields, and livestock.
There are additional precautions private well owners can take to reduce exposure risk to private well contaminants:
  • Periodically inspect exposed parts of wells for problems such as:
    • Cracked, corroded, or damaged well casings
    • Broken or missing well caps
    • Settling and cracking of surface seals
  • Slope areas around wells to drain surface runoff away
  • Install a well cap or sanitary seal to prevent unauthorized use of, or entry into, well
  • Have wells tested once a year for coliform bacteria, nitrates, and other constituents of concern
  • Keep accurate records of all well maintenance, especially disinfection or sediment removal, processes that may require use of chemicals
  • Hire a certified well driller for any new well construction, modification, abandonments or closures
  • Avoid mixing or using pesticides, fertilizers, herbicides, degreasers, fuels, and other pollutants near a well
  • Do not dispose of wastes in dry wells or in abandoned wells
  • Keep well casings a minimum of 12 inches above the ground’s surface
  • Pump and inspect septic systems as often as recommended by your local health department
  • Never dispose of harsh chemicals, solvents, petroleum products, or pesticides in a septic system or dry well

What can I do if I have a problem with my well?

Well owners may choose from four primary options for water treatment:
  • Disinfection of the well to eliminate bacteria should be done by a professional.
  • Note: In areas with naturally occurring arsenic in the groundwater, self chlorination should especially be avoided.
  • Point of use treatment, usually under the kitchen sink, to filter contaminants from drinking and cooking water
  • Point of entry treatment, usually at a point where the well water enters the home plumbing system
  • Multiple treatments for the household water system, usually near the water storage tank, to filter multiple contaminants or to improve water quality for all household uses
​Treatment systems must be properly maintained to ensure water quality. Most filter cartridges, membranes, or ultraviolet lights must be replaced at least once a year. Ask about maintenance needs before the water treatment system is installed. Then, keep accurate maintenance records and test both the treatment system and the water regularly.

How is private well water quality tracked?

The Colorado Environmental Public Health Tracking Program at the state health department compiles all publicly available well water quality data into a data repository and provides summary statistics based on these reported test results. Since there are no regulatory requirements for testing private well water, how often well water is tested and reported depends on many things and can be very inconsistent across counties. Public labs that regularly test well water samples provide data updates to CDPHE annually or semi-annually. Laboratories that operate as a private business often do not share the data they collect with the Colorado Environmental Public Health Tracking Program. Other well water data sets are the result of a one-time study or sampling event but have been included in the private well data repository to help fill data gaps.​