Public water system · SD4600370
ActiveWillow Lake
At a glance
Willow Lake (PWSID SD4600370) is an active community water system in Clark County, South Dakota. It reports serving 255 people through 163 service connections. Its primary water source is purchased groundwater, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in November 2020.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
255
Service connections
163
Primary source
GWP
Purchased groundwater
System type
CWS
Community water system
System record
How does Willow Lake compare with other water systems in Clark County?
By EPA's size categories, Willow Lake is a very small system (500 people or fewer). Clark County has 7 active public water systems, and Willow Lake is the 3rd-largest of them by population served. Its population served is about 56% below the county average of 582 people per system, and accounts for 6.3% of the 4,073 people reported by systems filed under the county. Across South Dakota, the 699 active systems average 1,387 people each. Nationally, the average active community water system reports serving 6,703 people, so Willow Lake is well below that figure.
What does “community water system” mean?
A community water system serves at least 15 connections used by year-round residents, or regularly serves at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these. South Dakota has 510 active community water systems, 73% of the state's 699 active systems. Purchased groundwater means the system buys groundwater from another public water system rather than drawing its own. 100 South Dakota systems (14%) list purchased groundwater as their primary source.
Who owns and regulates Willow Lake?
EPA lists Willow Lake as owned by a local government. The SD state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 3 of the 7 active systems in Clark County (43%) are also owned by a local government.
Does Willow Lake have drinking water violations?
Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in November 2020. The violations listed here began between August 1992 and November 2020. By type: 6 contaminant level above the legal limit, 4 required treatment not met and 2 monitoring and reporting. The contaminant or rule involved most often is Total coliform bacteria (TCR) (8 of them). EPA lists 10 as resolved and 2 as archived. Resolved means at least one resolving action is on record: the system returned to compliance, the rule no longer applies, or no further action was needed. Archived means the violation was not marked resolved but is more than five years past the end of the noncompliance period, so it no longer counts toward current compliance status.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2020-11-23 | Required treatment not metTreatment Technique No Certif. Operator · code 12 | Stage 1 Disinfectants and Disinfection Byproducts Rulecode 0400 | Yes | Resolved |
| 2015-02-01 | Required treatment not metTreatment Technique No Certif. Operator · code 12 | Stage 1 Disinfectants and Disinfection Byproducts Rulecode 0400 | Yes | Resolved |
| 2011-02-01 | Required treatment not metTreatment Technique No Certif. Operator · code 12 | Stage 1 Disinfectants and Disinfection Byproducts Rulecode 0400 | Yes | Resolved |
| 2006-02-23 | Required treatment not metTreatment Technique No Certif. Operator · code 12 | Stage 1 Disinfectants and Disinfection Byproducts Rulecode 0400 | Yes | Resolved |
| 2001-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1999-12-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1997-09-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1994-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1993-11-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1993-09-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1992-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1992-08-01 | Monitoring and reportingMonitoring, Repeat Minor (TCR) · code 26 | Total coliform bacteria (TCR)code 3100 | No | Archived |
The 12 most recent violations in EPA's records, newest first.Labels and codes come from EPA's SDWIS reference tables. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found. "Health-based" marks violations of a legal limit or required treatment.
Willow Lake: frequently asked questions
Who runs Willow Lake?
Willow Lake (PWSID SD4600370) is a community water system owned by a local government. It is regulated by the SD state drinking water program.
How many people does Willow Lake serve?
Willow Lake reports serving 255 people through 163 service connections in Clark County, South Dakota.
Where does Willow Lake get its water?
EPA SDWIS lists this system's primary water source as purchased groundwater. Purchased groundwater means the system buys groundwater from another public water system rather than drawing its own.
Does Willow Lake have any drinking water violations?
Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in November 2020. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found.
Is Willow Lake's water safe to drink?
AquaCensus shows EPA compliance records, not current water test results, so it cannot say whether the water is safe at a given moment. Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in November 2020. For current results, consult the system's annual water quality report, EPA ECHO, or the SD state drinking water program.
Where can I find Willow Lake's water quality report?
As a community water system, Willow Lake must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1 each year, covering the previous calendar year. The system can provide a copy on request.
Other water systems in Clark County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Clark Rural Water System | Clark + 3 more | 2,325 | Community | Groundwater |
| Clark | Clark | 1,148 | Community | Purchased groundwater |
| Fordham Colony | Clark | 142 | Community | Groundwater |
| Collins Colony | Clark | 95 | Community | Groundwater |
| Shamrock Colony | Clark | 75 | Community | Groundwater |
| Garden City | Clark | 33 | Community | Purchased groundwater |
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About this data
Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.
Cite as: AquaCensus, “Willow Lake, PWSID SD4600370, South Dakota”, https://aquacensus.com/water-systems/south-dakota/willow-lake-sd4600370 (data as of October 1, 2026).