01The verdict: is Boulder water safe?
Boulder's drinking water has significant quality concerns based on EPA testing data. With a grade of B+ (81.7/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 1 water system serves approximately 1,400 residents using groundwater (wells).
Copper is over its legal limit
Measured at 1.40 mg/L against the EPA Action Level of 1.3 mg/L. The ledger below shows how far over — and which filter removes it.
See the measurement ↓Lead is well under the limit
90th-percentile lead is 0.0 ppb — beneath the 15 ppb federal action level and under the 5 ppb watch threshold.
See the trend ↓3 violations in the last five years
Recent compliance history is the best predictor of future problems — the year-by-year record is below.
See the record ↓Boulder's drinking water received a grade of B+ (81.7 out of 100), indicating good water quality. The city's 1 water system serves approximately 1,400 residents using groundwater.
Lead levels were measured at 0.0 ppb (90th percentile), well within EPA limits. This system has not yet been tested for PFAS under the EPA UCMR 5 program. The system has 87 violations on record, including 6 health-based violations. 12 remain unresolved.
Boulder ranks #31 out of 110 cities in Montana for water quality, placing it mid-range in the state. Boulder relies on groundwater, which is generally less vulnerable to surface contamination but can be affected by naturally occurring minerals like arsenic and nitrate, as well as agricultural and industrial runoff. As a small community water system, Boulder may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
02What's in Boulder's water
Every contaminant flagged in Boulder, on one shared scale: distance to its own legal limit. The red line is the limit — anything past it is out of compliance, and the closer a bar gets, the less headroom the system has.
Over Limit — EPA Action Level: 1.3 mg/L
Exceeds the EPA action level. Copper leaches from household plumbing — flush taps for 30 seconds before drinking, and consider a certified filter.Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 0.0 | 15 | ppb | Inorganic | Safe |
| Copper (90th percentile) CopperInorganic A metal that enters drinking water mainly through corrosion of copper plumbing. Small amounts are essential for health, but excess levels are harmful. Health EffectsGastrointestinal distress (nausea, vomiting, diarrhea) at short-term high levels; liver and kidney damage from long-term exposure. EPA Limit1.3 mg/L action level Common SourcesCorrosion of copper household plumbing, erosion of natural deposits. | 1.40 | 1.3 | mg/L | Inorganic | Over Limit |
Cities ranked by 90th-percentile lead PF PFAS in Montana
Cities ranked by compounds detected Cu Copper in Montana
Cities ranked by 90th-percentile copper
03Boulder's ten-year track record
Each box is one year. A green check means no EPA violations; a numbered badge counts that year's violations — red if any were health-based, amber if they were monitoring or paperwork issues. The system has 87 violations on record, including 6 health-based violations. 12 remain unresolved.
7 of the last ten years were clean. The numbered years had EPA violations — red when any were health-based, amber when they were paperwork or missed-testing issues.
▼ Down 5.1 ppb since 2004. Latest reading: 0 ppb (2024) — 0% of the action level. Sampled at higher-risk homes (90th percentile).
▼ Down 2.0 mg/L since 1993. The latest reading (1.4 mg/L, 2009) is over the action level. Sampled at higher-risk homes (90th percentile).
04Where Boulder's water comes from
Boulder's drinking water is drawn from underground aquifers through wells.
Groundwater
Underground aquifers reached by wells — naturally filtered, but can carry minerals like arsenic and nitrate.
Local treatment
Groundwater generally needs less treatment — typically disinfection and, where needed, mineral removal.
1 system
1 water system, operated under local government ownership.
1,400 people
Residents served across Boulder's service area.
Groundwater is naturally filtered through rock and soil layers, generally requiring less treatment than surface water. However, it can contain naturally occurring contaminants like arsenic, radon, and minerals. Agricultural activity, septic systems, and industrial operations near well fields can introduce nitrates, pesticides, and volatile organic compounds. The system is operated by local government ownership and serves approximately 1,400 people through 1 water system.
| System name | PWSID | Population | Source |
|---|---|---|---|
| BOULDER CITY OF | MT0000158 | 1,400 | Groundwater |
Water bodies near Boulder
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on Boulder's watershed
Outside forces that shape what reaches the treatment plant. None of these is a verdict on the tap by itself — but each adds pressure worth knowing about.
Flood & storm history
4 federal disaster declarations on record for Jefferson County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
Drought
Jefferson County is in D2 (severe drought) per the U.S. Drought Monitor (week of Jul 2026). Drought can raise disinfection-byproduct levels and taste/odor issues as utilities draw from lower reservoirs.
06How Boulder compares
Scores for nearby Montana cities on one line, with the average marked.
dashed line = Montana average (48/100)
Boulder scores 81.7/100 — above the Montana average of 48/100. It outscores 9 of 10 nearby cities. Full Montana rankings →
39.6 / 100FMissoula, MT
42.6 / 100FBozeman, MT
43.4 / 100FGreat Falls, MT
34.5 / 100FKalispell, MT
40.1 / 100FHelena, MT
39.1 / 100
Compare all cities in the county — grades, violations, and contaminant data side by side.→
07What to do at home
Steps matched to what testing actually found in Boulder's water — not generic advice.
Filter drinking & cooking water
NSF-certified water filter. Copper exceeds the EPA action level of 1.3 mg/L
Compare tested filters →Read your utility's annual report
Every utility must publish a yearly Consumer Confidence Report with its own testing results. It pairs well with the independent data on this page.
How to read a CCR →Watch for Boulder alerts
This area has a history of flood declarations — after severe weather, watch for boil-water advisories from the utility, and check the live alerts on this page.
All water alerts →Frequently asked questions
Is Boulder, MT tap water safe to drink?
Boulder's water quality earned a grade of B+ (81.7/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #31 out of 110 cities tested in Montana.
What contaminants are in Boulder's water?
Lead was measured at 0.0 ppb (90th percentile). 87 violations are on record.
How is Boulder's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in Boulder?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Boulder's water come from?
Boulder's water is sourced from Groundwater. The city has 1 water system serving approximately 1,400 residents.
What health violations has Boulder's water system had?
Boulder has 6 health-based violations on record. The most recent violation was recorded in January 2024. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 12 violations remain unresolved.
Is Boulder's groundwater at risk of contamination?
Boulder uses groundwater, which can be affected by naturally occurring contaminants like arsenic, radon, and nitrate, as well as agricultural runoff and industrial activity. The system has 87 violations on record that may relate to groundwater quality. Groundwater systems are generally less susceptible to surface contamination but should be monitored for emerging contaminants like PFAS.
How does Boulder's water compare to other cities?
Boulder ranks #31 out of 110 cities in Montana (better than 72% of state cities) and #7271 out of 15382 cities nationally (53th percentile). The grade of B+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.
Does Boulder's small water system affect quality?
Boulder's system serves approximately 1,400 residents. Small community water systems (under 3,300 people) may have fewer financial resources for infrastructure upgrades and advanced treatment technologies. However, they are held to the same EPA drinking water standards as larger systems. This system has 87 violations on record.