Is Sister Bay, WI Tap Water Safe to Drink?
Graded B+, with 3 unresolved violations on record. See what was cited — and what it means for your tap. What to do next ↓
82.5/100
waterverge.com Sister Bay, WI — Water Quality Report
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.
What to know about Sister Bay's water
Sister Bay ranks #218 out of 446 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.
Water quality score
See methodology →Is Sister Bay, WI water safe to drink?
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).
Recent water quality updates for Sister Bay
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Sister Bay's water quality assessment. Grade: B+ (82.5/100).
Contaminants: Consumer Confidence Rule.
Federal disaster declaration (FEMA DR-3249). Hurricane event — may have impacted local water infrastructure.
Contaminants: Consumer Confidence Rule.
Contaminants: Coliform (TCR).
Federal disaster declaration (FEMA DR-376). Flood event — may have impacted local water infrastructure.
Key contaminant findings
Based on the most recent EPA sampling data for Sister Bay's water supply.
Within EPA limits but above the American Academy of Pediatrics recommended level of 1 ppb. An NSF 53-certified filter provides additional protection.
Violation history
Sister Bay's water system has 4 total violations on record, including 0 health-based violations. 3 remain unresolved.
Flood & environmental risk
Door County has experienced 2 federally declared disasters since 1973. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies.
Where does Sister Bay's water come from?
Sister Bay's drinking water comes from groundwater (wells), supplied by 1 water system serving approximately 1,000 people. Groundwater is generally less susceptible to surface contamination but can contain naturally occurring contaminants like arsenic, radon, and nitrate.
What Sister Bay residents can do
Recommended: NSF-certified water filter. This addresses the specific contaminants found in Sister Bay's water.
Your water utility is required to publish an annual Consumer Confidence Report (CCR) with detailed testing results. Ask for the latest copy or check your utility's website.
Run cold water for 30 seconds before drinking, especially in the morning. Lead and copper leach from household plumbing when water sits in pipes.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Violation summary
Violations & advisories
Flood & disaster history
Door County has experienced 2 federally declared disasters since 1973. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Recommended water filters
Based on contaminants detected in Sister Bay's water supply, we recommend the following filter types.
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 |
Lead level trend (90th percentile)
See how Sister Bay compares by contaminant
Explore where Sister Bay ranks among all Wisconsin cities for specific contaminants.
Water source & infrastructure
Where Sister Bay's water comes from
Sister Bay's drinking water is drawn from underground aquifers through wells.
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.
Water systems serving Sister Bay
| System Name | PWSID | Population | Source |
|---|---|---|---|
| SISTER BAY WATERWORKS | WI4150510 | 1,000 | GW |
How Sister Bay compares
Full Wisconsin rankings →Sister Bay's score of 82.5/100 is above the average of 65/100 among major Wisconsin cities. It outscores 7 of 10 nearby cities.
Nearby cities
View Wisconsin rankings →About Sister Bay, WI
Learn more about your water
Guides and resources related to Sister Bay's water quality findings.
Explore water quality across Door
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 446 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 446 cities in Wisconsin (better than 51% of state cities) and #6934 out of 15744 cities nationally (56th 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.