Public water system · WA5360190
ActiveTwanoh Terrace Water Co
At a glance
Twanoh Terrace Water Co (PWSID WA5360190) is an active community water system in Mason County, Washington. It reports serving 75 people through 30 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, none is health-based, and the most recent began in January 2008.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
75
Service connections
30
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Twanoh Terrace Water Co compare with other water systems in Mason County?
By EPA's size categories, Twanoh Terrace Water Co is a very small system (500 people or fewer). Mason County has 240 active public water systems. Its population served is well below the county average of 315 people per system, and accounts for less than 0.1% of the 75,633 people reported by systems filed under the county. Across Washington, the 4,705 active systems average 2,172 people each. Nationally, the average active community water system reports serving 6,703 people, so Twanoh Terrace Water Co 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. Washington has 2,392 active community water systems, 51% of the state's 4,705 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 4,370 Washington systems (93%) list groundwater as their primary source.
Who owns and regulates Twanoh Terrace Water Co?
EPA lists Twanoh Terrace Water Co as owned by a local government. The WA state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 64 of the 240 active systems in Mason County (27%) are also owned by a local government.
Does Twanoh Terrace Water Co have drinking water violations?
Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in January 2008. The violations listed here began between October 2006 and January 2008. By type: 12 monitoring and reporting. The contaminant or rule involved most often is 1,2-Dibromo-3-chloropropane (DBCP) (3 of them). EPA lists 9 as resolved and 3 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 |
|---|---|---|---|---|
| 2008-01-01 | Monitoring and reportingInitial Tap Sampling for Pb and Cu · code 51 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2007-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | 1,2-Dibromo-3-chloropropane (DBCP)code 2931 | No | Archived |
| 2007-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | Ethylene dibromide (EDB)code 2946 | No | Archived |
| 2007-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | Diquatcode 2032 | No | Resolved |
| 2007-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 2007-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Diquatcode 2032 | No | Resolved |
| 2007-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Ethylene dibromide (EDB)code 2946 | No | Resolved |
| 2007-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | 1,2-Dibromo-3-chloropropane (DBCP)code 2931 | No | Resolved |
| 2006-12-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 2006-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | 1,2-Dibromo-3-chloropropane (DBCP)code 2931 | No | Resolved |
| 2006-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Diquatcode 2032 | No | Resolved |
| 2006-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Ethylene dibromide (EDB)code 2946 | 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.
Twanoh Terrace Water Co: frequently asked questions
Who runs Twanoh Terrace Water Co?
Twanoh Terrace Water Co (PWSID WA5360190) is a community water system owned by a local government. It is regulated by the WA state drinking water program.
How many people does Twanoh Terrace Water Co serve?
Twanoh Terrace Water Co reports serving 75 people through 30 service connections in Mason County, Washington.
Where does Twanoh Terrace Water Co 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 Twanoh Terrace Water Co have any drinking water violations?
Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in January 2008. 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 Twanoh Terrace Water Co'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, none is health-based, and the most recent began in January 2008. For current results, consult the system's annual water quality report, EPA ECHO, or the WA state drinking water program.
Where can I find Twanoh Terrace Water Co's water quality report?
As a community water system, Twanoh Terrace Water Co 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 Mason County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Shelton City of | Mason | 15,089 | Community | Groundwater |
| Belfair Water District 1 | Mason | 4,432 | Community | Groundwater |
| Lake Cushman System 5 | Mason | 3,675 | Community | Groundwater |
| Twanoh State Park | Mason | 3,173 | Transient non-community | Groundwater |
| Belfair State Park | Mason | 2,411 | Transient non-community | Groundwater |
| Timberlake Community Club Inc. | Mason | 2,337 | 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, “Twanoh Terrace Water Co, PWSID WA5360190, Washington”, https://aquacensus.com/water-systems/washington/twanoh-terrace-water-co-wa5360190 (data as of October 1, 2026).