01The verdict: is Sister Bay water safe?
Sister Bay's drinking water has significant quality concerns based on EPA testing data. With a grade of B+ (82.5/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 1 water system serves approximately 1,000 residents using groundwater (wells).
3 unresolved violations on record
EPA records show open compliance items for this system. Most are administrative, but unresolved items are worth watching.
See what was cited ↓Top half in Wisconsin
Sister Bay ranks #218 of 441 graded Wisconsin cities.
See the comparison ↓Check back after the next refresh
EPA data updates on a rolling basis; we fold in new samples and violations every month.
Get alerts ↓Sister Bay's drinking water received a grade of B+ (82.5 out of 100), indicating good water quality. The city's 1 water system serves approximately 1,000 residents using groundwater.
Lead levels were measured at 6.1 ppb (90th percentile), which is within EPA limits but above recommended levels. This system has not yet been tested for PFAS under the EPA UCMR 5 program. The system has 4 violations on record, including 0 health-based violations. 3 remain unresolved.
Sister Bay ranks #218 out of 441 cities in Wisconsin for water quality, placing it mid-range in the state. Sister Bay 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. While lead levels are within EPA limits, they are above the recommended 5 ppb threshold that health organizations consider ideal. A point-of-use filter adds an extra layer of protection. As a small community water system, Sister Bay may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
02What's in Sister Bay's water
Every contaminant flagged in Sister Bay, 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.
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. | 6.1 | 15 | ppb | Inorganic | Safe |
Cities ranked by 90th-percentile lead PF PFAS in Wisconsin
Cities ranked by compounds detected Cu Copper in Wisconsin
Cities ranked by 90th-percentile copper
03Sister Bay'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 4 violations on record, including 0 health-based violations. 3 remain unresolved.
All ten of the last ten years were clean — no EPA violations recorded for Sister Bay.
▲ Up 1.1 ppb since 1993. Latest reading: 6.1 ppb (2023) — 41% of the action level. Sampled at higher-risk homes (90th percentile).
04Where Sister Bay's water comes from
Sister Bay'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.
1,000 people
Residents served across Sister Bay'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 1,000 people through 1 water system.
| System name | PWSID | Population | Source |
|---|---|---|---|
| SISTER BAY WATERWORKS | WI4150510 | 1,000 | Groundwater |
05Pressure on Sister Bay'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
2 federal disaster declarations on record for Door County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
06How Sister Bay compares
Scores for nearby Wisconsin cities on one line, with the average marked.
dashed line = Wisconsin average (65/100)
Sister Bay scores 82.5/100 — above the Wisconsin average of 65/100. It outscores 7 of 10 nearby cities. Full Wisconsin rankings →
90.2 / 100FMadison, WI
35.4 / 100DGreen Bay, WI
54 / 100CRacine, WI
69.5 / 100DKenosha, WI
45.8 / 100DWaukesha, WI
47.1 / 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 Sister Bay's water — not generic advice.
Filter drinking & cooking water
NSF-certified water filter. Lead detected at 6.1 ppb
Compare tested filters →Flush taps & check your service line
Lead leaches from pipes as water sits. Run cold water 30 seconds before drinking (especially mornings), and ask the utility whether your address still has a lead service line.
Lead risks explained →Watch for Sister Bay alerts
We refresh EPA data monthly and surface new violations, advisories, and boil-water notices for your county on this page.
All water alerts →Frequently asked questions
Is Sister Bay, WI tap water safe to drink?
Sister Bay's water quality earned a grade of B+ (82.5/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #218 out of 441 cities tested in Wisconsin.
What contaminants are in Sister Bay's water?
Lead was measured at 6.1 ppb (90th percentile). 4 violations are on record.
How is Sister Bay'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 Sister Bay?
While lead levels are within EPA limits, a filter adds extra protection. Based on current data, basic filtration should suffice for additional peace of mind.
Where does Sister Bay's water come from?
Sister Bay's water is sourced from Groundwater. The city has 1 water system serving approximately 1,000 residents.
Is Sister Bay's groundwater at risk of contamination?
Sister Bay 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 4 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 Sister Bay's water compare to other cities?
Sister Bay ranks #218 out of 441 cities in Wisconsin (better than 51% of state cities) and #6877 out of 15382 cities nationally (55th percentile). The grade of B+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.
Does Sister Bay's small water system affect quality?
Sister Bay's system serves approximately 1,000 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 4 violations on record.