01The verdict: is Cass Lake water safe?
Cass Lake's drinking water has significant quality concerns based on EPA testing data. With a grade of C- (56.1/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 8 water systems serve approximately 3,588 residents using groundwater (wells).
Copper is over its legal limit
Measured at 1.67 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 ↓23 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 ↓Cass Lake's drinking water received a grade of C- (56.1 out of 100), indicating poor water quality. The city's 8 water systems serve approximately 3,588 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 142 violations on record, including 17 health-based violations. 25 remain unresolved.
Cass Lake ranks #455 out of 466 cities in Minnesota for water quality, placing it among the lowest-rated in the state. Cass Lake 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. The system has seen 23 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
02What's in Cass Lake's water
Every contaminant flagged in Cass Lake, 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. | 1.67 | 1.3 | mg/L | Inorganic | Over Limit |
Cities ranked by 90th-percentile lead PF PFAS in Minnesota
Cities ranked by compounds detected Cu Copper in Minnesota
Cities ranked by 90th-percentile copper
03Cass Lake'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 142 violations on record, including 17 health-based violations. 25 remain unresolved.
4 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.
▲ Up 1.1 ppb since 2004. Latest reading: 1.1 ppb (2025) — 8% of the action level. Sampled at higher-risk homes (90th percentile).
1.7mg/L(2022)
One sampling round on record — 128% of the 1.3mg/L EPA action level. Sampled at higher-risk homes (90th percentile).
04Where Cass Lake's water comes from
Cass Lake'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.
8 systems
8 water systems, operated under native american ownership.
3,588 people
Residents served across Cass Lake'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 native american ownership and serves approximately 3,588 people through 8 water systems.
| System name | PWSID | Population | Source |
|---|---|---|---|
| NORTHSIDE | 055294214 | 2,086 | Groundwater |
| Cass Lake | MN1110006 | 691 | Groundwater |
| BALL CLUB | 055294201 | 333 | Groundwater |
| INGER | 055294204 | 186 | Groundwater |
| BENA | 055294202 | 112 | Groundwater |
| PLANTATION | 055294205 | 105 | Groundwater |
| OAK POINT | 055294207 | 45 | Groundwater |
| OLD AGENCY | 055294208 | 30 | Groundwater |
Water bodies near Cass Lake
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on Cass Lake'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.
Industrial discharge
1 facility within 10 miles reported 0 lb released to surface water in the latest EPA Toxics Release Inventory. Proximity doesn't equal tap contamination — treatment and hydrology decide — but it's pressure on the watershed.
Flood & storm history
6 federal disaster declarations on record for Cass County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
Superfund proximity
1 National Priorities List site within 10 miles. Proximity does not necessarily indicate tap-water contamination — the connection depends on hydrology and treatment.
Drought
Cass 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 Cass Lake compares
Scores for nearby Minnesota cities on one line, with the average marked.
dashed line = Minnesota average (82/100)
Cass Lake scores 56.1/100 — below the Minnesota average of 82/100. Full Minnesota rankings →
72.8 / 100BSt. Paul, MN
73.3 / 100CRochester, MN
69.7 / 100ABloomington, MN
93.6 / 100BBrooklyn Park, MN
81.5 / 100ADuluth, MN
88.6 / 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 Cass Lake'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 Cass Lake 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 Cass Lake, MN tap water safe to drink?
Cass Lake's water quality earned a grade of C- (56.1/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #455 out of 466 cities tested in Minnesota.
What contaminants are in Cass Lake's water?
Lead was measured at 0.0 ppb (90th percentile). 142 violations are on record.
How is Cass Lake'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 Cass Lake?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Cass Lake's water come from?
Cass Lake's water is sourced from Groundwater. The city has 8 water systems serving approximately 3,588 residents.
What health violations has Cass Lake's water system had?
Cass Lake has 17 health-based violations on record. The most recent violation was recorded in October 2024. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 25 violations remain unresolved.
Is Cass Lake's groundwater at risk of contamination?
Cass Lake 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 142 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 Cass Lake's water compare to other cities?
Cass Lake ranks #455 out of 466 cities in Minnesota (better than 2% of state cities) and #12262 out of 15382 cities nationally (20th percentile). The grade of C- reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.