Public water system · SD4601082

Active

Keystone

At a glance

Keystone (PWSID SD4601082) is an active community water system in Pennington County, South Dakota. It reports serving 349 people through 249 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 4 are health-based, and the most recent began in January 2019.

Dataset updated October 2026 . Source: EPA SDWIS/ECHO public records.

Population served

349

Service connections

249

Primary source

Groundwater

System type

CWS

Community water system

System record

PWSIDSD4601082

System typeCommunity water system

Activity statusActive

Population served349

Service connections249

Primary water sourceGroundwater

Owner typeLocal government

Primacy agencySD state drinking water program

City servedKeystone

StateSouth Dakota

ZIP57751

CountyPennington County

How does Keystone compare with other water systems in Pennington County?

By EPA's size categories, Keystone is a very small system (500 people or fewer). Pennington County has 150 active public water systems. Its population served is about 62% below the county average of 930 people per system, and accounts for 0.3% of the 139,467 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 Keystone 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. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 431 South Dakota systems (62%) list groundwater as their primary source.

Who owns and regulates Keystone?

EPA lists Keystone 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. 12 of the 150 active systems in Pennington County (8%) are also owned by a local government.

Does Keystone have drinking water violations?

Of the 12 most recent violations in EPA's records, 4 are health-based, and the most recent began in January 2019. The violations listed here began between November 1989 and January 2019. By type: 7 monitoring and reporting, 4 contaminant level above the legal limit and 1 public notice, recordkeeping or other. The contaminant or rule involved most often is Total coliform bacteria (TCR) (4 of them). EPA lists 12 as resolved. 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.

Began	Violation	Contaminant or rule	Health-based	Status
2019-01-01	Monitoring and reportingMonitoring, Regular · code 03	Combined Uraniumcode 4006	No	Resolved
2019-01-01	Monitoring and reportingMonitoring, Regular · code 03	Gross alpha (excluding radon and uranium)code 4000	No	Resolved
2019-01-01	Monitoring and reportingMonitoring, Regular · code 03	Combined Radium (-226 and -228)code 4010	No	Resolved
2015-10-01	Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22	Total coliform bacteria (TCR)code 3100	Yes	Resolved
2015-09-01	Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22	Total coliform bacteria (TCR)code 3100	Yes	Resolved
2015-06-01	Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22	Total coliform bacteria (TCR)code 3100	Yes	Resolved
2010-10-01	Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52	Lead and Copper Rulecode 5000	No	Resolved
2000-07-01	Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71	Consumer Confidence Rulecode 7000	No	Resolved
1995-09-01	Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22	Total coliform bacteria (TCR)code 3100	Yes	Resolved
1989-11-08	Monitoring and reportingMonitoring, Regular · code 03	Bariumcode 1010	No	Resolved
1989-11-08	Monitoring and reportingMonitoring, Regular · code 03	Mercurycode 1035	No	Resolved
1989-11-08	Monitoring and reportingMonitoring, Regular · code 03	Fluoridecode 1025	No	Resolved

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.

Keystone: frequently asked questions

Who runs Keystone?

Keystone (PWSID SD4601082) is a community water system owned by a local government. It is regulated by the SD state drinking water program.

How many people does Keystone serve?

Keystone reports serving 349 people through 249 service connections in Pennington County, South Dakota.

Where does Keystone get its water?

EPA SDWIS lists this system's primary water source as groundwater. Groundwater means the system draws its water from wells or springs fed by underground aquifers.

Does Keystone have any drinking water violations?

Of the 12 most recent violations in EPA's records, 4 are health-based, and the most recent began in January 2019. 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 Keystone'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, 4 are health-based, and the most recent began in January 2019. For current results, consult the system's annual water quality report, EPA ECHO, or the SD state drinking water program.

Where can I find Keystone's water quality report?

As a community water system, Keystone 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 Pennington County

Water system	County	Population served	Type	Source
Rapid City	Pennington	72,009	Community	Surface water
Box Elder	Pennington	14,000	Community	Groundwater
Rapid Valley Sanitary District	Pennington	11,408	Community	Surface water
Ellsworth Afb	Pennington	9,100	Community	Purchased surface water
Nps-Mount Rushmore National Memorial	Pennington	4,100	Non-transient non-community	Groundwater
Colonial Pine Hills Sanitary Distric	Pennington	1,200	Community	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, “Keystone, PWSID SD4601082, South Dakota”, https://aquacensus.com/water-systems/south-dakota/keystone-sd4601082 (data as of October 1, 2026).