Public water system · WA5357250
ActiveMountlake Terrace City of
At a glance
City of Mountlake Terrace (PWSID WA5357250) is an active community water system in Snohomish County, Washington. It reports serving 26,402 people through 9,290 service connections. Its primary water source is purchased surface water, 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 July 2024.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
26,402
Service connections
9,290
Primary source
SWP
Purchased surface water
System type
CWS
Community water system
System record
How does City of Mountlake Terrace compare with other water systems in Snohomish County?
By EPA's size categories, City of Mountlake Terrace is a large system (10,001 to 100,000 people). Snohomish County has 167 active public water systems. Its population served is about 4.3 times the county average of 6,200 people per system, and accounts for 2.5% of the 1,035,433 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 City of Mountlake Terrace is about 3.9 times 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. Purchased surface water means the system buys surface water from another public water system rather than drawing its own. 130 Washington systems (2.8%) list purchased surface water as their primary source.
Who owns and regulates City of Mountlake Terrace?
EPA lists City of Mountlake Terrace 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. 36 of the 167 active systems in Snohomish County (22%) are also owned by a local government.
Does City of Mountlake Terrace have drinking water violations?
Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in July 2024. The violations listed here began between September 1992 and July 2024. By type: 8 public notice, recordkeeping or other and 4 monitoring and reporting. The contaminant or rule involved most often is Consumer Confidence Rule (8 of them). EPA lists 11 as resolved and 1 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 |
|---|---|---|---|---|
| 2024-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2020-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Resolved |
| 2020-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Haloacetic acids (HAA5)code 2456 | No | Resolved |
| 2019-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Resolved |
| 2017-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2016-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2015-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2014-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2013-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2012-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 2011-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | Resolved |
| 1992-09-01 | 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.
City of Mountlake Terrace: frequently asked questions
Who runs City of Mountlake Terrace?
City of Mountlake Terrace (PWSID WA5357250) is a community water system owned by a local government. It is regulated by the WA state drinking water program.
How many people does City of Mountlake Terrace serve?
City of Mountlake Terrace reports serving 26,402 people through 9,290 service connections in Snohomish County, Washington.
Where does City of Mountlake Terrace get its water?
EPA SDWIS lists this system's primary water source as purchased surface water. Purchased surface water means the system buys surface water from another public water system rather than drawing its own.
Does City of Mountlake Terrace 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 July 2024. 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 City of Mountlake Terrace'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 July 2024. For current results, consult the system's annual water quality report, EPA ECHO, or the WA state drinking water program.
Where can I find City of Mountlake Terrace's water quality report?
As a community water system, City of Mountlake Terrace 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 Snohomish County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Alderwood Water District | Snohomish | 245,715 | Community | Purchased surface water |
| Everett Public Works Dept. City of | Snohomish | 215,774 | Community | Surface water |
| Marysville Utilities | Snohomish | 88,582 | Community | Purchased surface water |
| Lynnwood City of | Snohomish | 68,204 | Community | Purchased surface water |
| Sno PUD 1 - Lake Stevens | Snohomish | 67,710 | Community | Purchased surface water |
| Silver Lake Water & Sewer District | Snohomish | 65,033 | Community | Purchased surface water |
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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, “Mountlake Terrace City of, PWSID WA5357250, Washington”, https://aquacensus.com/water-systems/washington/mountlake-terrace-city-of-wa5357250 (data as of October 1, 2026).