Waukesha's Water: From Radium to Lake Michigan
Data source: EPA SDWIS, Wisconsin DNR, Great Lakes-St. Lawrence River Basin Water Resources Council
For more than two decades, the city of Waukesha, Wisconsin had a radium problem. Not a small one. Its groundwater wells were pulling up water laced with naturally occurring radium at levels that violated federal standards — and the city spent millions of dollars treating water it could not fully fix.
In October 2023, that chapter ended. Waukesha completed a full switch to Lake Michigan water, becoming the first city outside the Great Lakes basin to receive a diversion approval under the Great Lakes Compact. The EPA violation record at ZIP code 53186 tells the story in data: 126 Gross Beta violations, 100 Gross Alpha violations, 11 Radium-228 violations — all accumulated over decades of groundwater reliance.
The Radium Problem, Explained
Radium is a naturally occurring radioactive element that forms when uranium and thorium in bedrock decay. It dissolves into groundwater, and its concentration typically increases the deeper you drill. As communities grow and demand more water, wells go deeper — and radium levels rise.
Waukesha's problem began showing up clearly in the 1990s. Seven of the city's groundwater wells registered elevated radium. The EPA tightened its radium standard, and Waukesha found itself in violation. The city contested the new rules — filing a lawsuit against the EPA that lasted twelve years — but ultimately could not escape the geology beneath it.
The contamination wasn't unique to Waukesha. A 2016 investigation by Wisconsin Watch found radium levels rising in groundwater systems across the state as wells drilled deeper into the Cambrian aquifer. But Waukesha, with a service population of over 70,000, was the largest and highest-profile case.
A Decade of Negotiating the Impossible
The Great Lakes Compact, signed in 2008, is designed to keep Great Lakes water in the Great Lakes basin. Waukesha sits just outside the basin divide — close enough to see Milwaukee, far enough to be legally excluded.
The city applied for a diversion exception in 2010. The process required approval from all eight Great Lakes states. It took six years of negotiations, environmental reviews, and public comment. In June 2016, the Great Lakes-St. Lawrence River Basin Water Resources Council unanimously approved Waukesha's request — with conditions.
The key terms: Waukesha could divert up to 8.2 million gallons per day from Lake Michigan (purchased from Milwaukee Water Works). All treated wastewater must be discharged to the Root River, which flows back into Lake Michigan via the Fox River. The city's service area was frozen — no using the Lake Michigan water as an excuse to expand development beyond existing boundaries.
Wisconsin DNR issued its formal diversion approval in 2021, after the full permitting process was complete.
Construction and Transition
Getting the water from Lake Michigan to Waukesha required building new infrastructure: a booster pumping station, transmission mains, and connections to Milwaukee's distribution system. Construction was substantial — the Great Water Alliance project used HDPE pipe systems to minimize disruption and ensure long-term durability.
The city began commissioning the new system on August 15, 2023. By October 9, 2023, the transition was complete — two weeks ahead of schedule. All groundwater wells were removed from active service. Most residents reported no discolored water or unusual smell during the switchover.
The water quality change was immediate and measurable. Lake Michigan water is roughly 60% softer than the groundwater it replaced. Milwaukee Water Works, which supplies the purchased water, tests for over 500 substances and operates one of the most extensive monitoring programs of any municipal water utility in the country.
What the Data Shows Now
EPA SDWIS records for Waukesha (53186) carry the weight of the pre-diversion era: 302 total violations across all water systems in the ZIP, 237 of which are health-based. The violation history is dominated by Gross Beta (126 violations), Gross Alpha (100 violations), and Radium-228 (11 violations) — all attributable to the former groundwater wells.
The most recent CCR data for Waukesha Water Utility (PWSID WI2680238), parsed from EPA records, shows Gross Alpha at 7.41 pCi/L against a Maximum Contaminant Level of 15 pCi/L. That reading reflects post-transition conditions: the system is now drawing from Lake Michigan, not the deep aquifer.
Waukesha is one of 5,572 US public water utilities tracked in the CCR Rich Dataset — and one of the 51.2% that disclose a customer-service phone number in their published Consumer Confidence Report.
As of mid-2024, the Waukesha Water Utility was in compliance with federal health-based standards, according to EPA monitoring records.
The historical violation count will remain in EPA databases — violations are not erased, they are resolved. Of the 302 total violations, 106 are marked resolved. The unresolved count (196) includes older records and monitoring/reporting violations that post-date the radium era.
The Home Safety Score for 53186 currently stands at 53 (Grade D), reflecting both the historical violation burden and other risk factors including radon (Zone 2, moderate risk) and flood exposure.
Why This Case Matters Beyond Waukesha
Waukesha is not an isolated story. The same Cambrian aquifer that fed Waukesha's wells runs beneath dozens of Wisconsin communities. A 2020 study found rising radium levels across southeastern Wisconsin's groundwater systems, particularly as residential growth pushes wells deeper.
The city's diversion also set a precedent. Waukesha's application is the only one ever approved under the Great Lakes Compact's exception process. Environmental groups continue to debate whether the approval was too permissive; water managers in other communities watch closely to see whether similar applications might follow.
For the ~70,000 people served by Waukesha Water Utility, the practical outcome is simpler: water that no longer exceeds radium standards, drawn from one of the largest freshwater lakes in the world.
Data on ZipCheckup
The full compliance history, contaminant breakdown, lead levels, and home safety score for Waukesha are available on the ZIP 53186 water quality report.
Wisconsin state-level data — including all water systems, violation trends, and county rankings — is available on the Wisconsin water quality page.
Data sources: EPA Safe Drinking Water Information System (SDWIS) via Envirofacts API; Wisconsin DNR Waukesha Diversion records; Great Lakes-St. Lawrence River Basin Water Resources Council 2016 decision; Wisconsin DNR 2023 and 2024 Waukesha Diversion Annual Reports. CCR data for PWSID WI2680238 parsed from EPA API records.
Frequently Asked Questions
Does Waukesha still have radium in its water?
Since October 2023, Waukesha Water Utility has been fully supplied by Lake Michigan water purchased from Milwaukee Water Works. The groundwater wells that showed radium contamination were removed from active service. The 2024 CCR data from EPA shows current Gross Alpha at 7.41 pCi/L — below the 15 pCi/L MCL.
When did Waukesha switch to Lake Michigan water?
The transition was completed on October 9, 2023 — two weeks ahead of schedule. The diversion was approved by the Great Lakes-St. Lawrence River Basin Water Resources Council in 2016. Construction of the water supply infrastructure was completed earlier in 2023, and commissioning began August 15, 2023.
How many EPA violations did Waukesha Water Utility accumulate?
EPA records show 302 total violations for water systems in ZIP code 53186, including 237 health-based violations. The bulk of these — 126 Gross Beta and 100 Gross Alpha violations — reflect the decades-long radium contamination of groundwater wells before the Lake Michigan switch.
Is Waukesha tap water safe now?
As of mid-2024, the Waukesha Water Utility was in compliance with federal health-based drinking water standards, according to EPA. Lake Michigan water purchased from Milwaukee Water Works undergoes testing for over 500 substances. The water is also roughly 60% softer than the previous groundwater source.
What was the Great Lakes Compact diversion for Waukesha?
The Great Lakes Compact normally prohibits diversions of Great Lakes water outside the basin. Waukesha sits just outside the basin boundary and was granted an exception in 2016 — the first such diversion approval under the Compact — for up to 8.2 million gallons per day, with a requirement to return treated wastewater to the Root River, which drains to Lake Michigan.