Well water testing in Boulder County, Colorado

What to test for in Boulder County

Private wells are not regulated like public water: EPA advises owners to test their well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Your state's own schedule:

• Colorado's health department (CDPHE) recommends testing every year for total coliform bacteria, total dissolved solids, nitrate/nitrite and pH, and every 3 to 5 years for arsenic, copper, fluoride, hardness, iron, lead, manganese and uranium. For a new well or a well with no known testing, it lists a broader panel that includes PFAS and a volatile organic compound (VOC) screen. It says more frequent testing may be needed if pregnant or breastfeeding people, small children or elderly adults drink the water. source
• CDPHE also says to test if someone in the home becomes pregnant or a child moves in, if people get unexplained stomach illness, if contaminants are found in a neighbor's well, if the water's taste, odor, color or clarity changes, after a spill near the well, after any well repair or part replacement, and after a nearby flood or fire. In areas with historic mining, it suggests you may consider a general metals panel. source
• Colorado State University Extension says wells used for drinking water should be tested for coliform bacteria every one to two years, along with other water quality parameters, and more often if the well is in poor condition, has been flooded, the septic system has failed, abandoned wells or feed yards are nearby, or visitors have had stomach or intestinal trouble. Its well-care checklist also says to have the well tested once a year for coliform bacteria, nitrate and other contaminants of concern. source

Arsenic. USGS estimates that about 73 people using private wells in Boulder County had arsenic above 10 µg/L, EPA's limit for public water (2010 base year; 95% range 53 to 102). USGS describes this kind of estimate as useful "for broad screening of the population at risk", so it says nothing certain about any one well. Arsenic has no taste or smell: test for it by name.

Radon. EPA puts Boulder County in Zone 1: highest potential (average indoor radon may be greater than 4 pCi/L). That map is about radon in indoor air, and EPA says it should not be used to decide whether an individual home needs testing. If radon is found in your air and you have a well, EPA suggests testing the water too: see radon in well water.

For anything specific to your home (farms nearby, old plumbing, a new baby, a smell or stain), use the which-tests checklist. When the results arrive, check your numbers against EPA's limits.

PFAS in public water near Boulder County (public supply, not your well)

Under EPA’s fifth Unregulated Contaminant Monitoring Rule (UCMR 5), public water systems sampled their water for 29 PFAS between Jan 3, 2023 and Jun 17, 2026. 10 public systems that serve ZIP codes mainly in Boulder County reported results. 1 of them had at least one sample with PFOA or PFOS at or above 4.0 ng/L, and 1 had at least one of the 29 PFAS measured at or above its reporting level.

4.0 ng/L (parts per trillion) is both EPA’s UCMR 5 reporting level for PFOA and PFOS and the number in EPA’s 2024 limit for public water. That limit is judged on a running annual average, so one sample at that level is not a violation. EPA proposed changes to its PFAS rules in May 2026: see PFAS in well water for the current status and who should test a well. To test your own well, find a lab certified for PFAS.

Method: a system counts for this county when it reports serving a ZIP code whose largest land part is in this county, so a system serving several counties counts in each. Source: U.S. EPA, UCMR 5 occurrence data (by state), file dated Oct 15, 2026; downloaded Nov 1, 2026.

Testing programs and help in Colorado

• Anyone with a private well in Colorado can apply to CDPHE's PFAS Testing and Assistance Program (PFAS TAP) for free PFAS testing: a kit is mailed to you, you collect the sample and mail it back with a prepaid label. Households that use the well for drinking and cooking and have PFAS above EPA's drinking water standard can get a free filter dispenser and one year of replacement filters; results from an independent lab test can also qualify. CDPHE says the program is available while supplies last. In 2026 it is doing targeted outreach with Boulder County and the San Luis Valley. source
• CDPHE says your local public health agency may offer annual water testing, and suggests contacting it or CDPHE's ToxCall line with questions about what to test for. source
• CDPHE publishes a list of labs it has confirmed can test private well water. It does not endorse any lab, says the list is not exhaustive, and recommends calling the lab to confirm the method, contaminants and price. It notes that results from some labs may not meet the criteria for state or federal assistance programs. source
• CDPHE's online well water tool lets you enter your lab results and compare them with drinking water guidelines. CDPHE notes that drinking water standards do not apply to private wells, but you can still use them to assess your water. source

Buying a home with a well in Boulder County

State-certified labs in Boulder County

Labs on the Colorado list whose own websites say they take homeowner samples: Colorado State University (Fort Collins), Three Lakes W/S District (Grand Lake). Use Check my ZIP to sort labs by distance.

See all Colorado labs in the finder and filter by the test you need and by labs that take homeowner samples.