Tapcensus

TTHM (Total Trihalomethanes) violations in Washington

212 active public water systems in Washington had a TTHM (Total Trihalomethanes) violation in the past three years, 22 of them in the latest quarter of EPA's data. What TTHM (Total Trihalomethanes) is and why it matters.

Health effects: Long-term exposure is associated with increased bladder cancer risk. Some studies link high TTHM exposure to adverse reproductive outcomes. Bromodichloromethane is classified as a possible human carcinogen.

Systems with a TTHM (Total Trihalomethanes) violation

Latest quarter first, then largest first
SystemServesStatusRules violated, 3 yrUnresolved
First Potholes Water Users Assn
Grant County 		90 2 0
Fairview Domestic Water Assn
Adams County 		89 2 0
Madison Estates
Tulalip · County 		86 1 0
San Poil
Keller · County 		86 5 0
Ferndale Estates LLC
Whatcom County 		85 2 0
Spring Point Homeowners Association
San Juan County 		85 1 0
Summerland
Island County 		85 3 0
Widarama Beach Water Rights Assn.
Island County 		85 2 0
Murphy Elma Veneer
Grays Harbor County 		80 1 0
Camano Shores Community
Island County 		79 1 0
Fort Knox Mobile Home Park
Island County 		79 1 0
Scenic Heights W a INC
Island County 		78 2 0
Vel View Water Dist 13
Spokane County 		77 3 0
Eastgate
Island County 		76 2 0
Peoples Creek Water System
Snohomish County 		76 1 0
Goosehaven
Pend Oreille County 		75 1 0
Island Ptba Water System
Island County 		75 1 0
Lake Wilderness Shore Acres Estate
King County 		75 5 0
Silver Lake RD Acreage Tracts
Island County 		73 1 0
Mabana Shores Association
Island County 		68 3 0
Fir Grove Mobile Park
Island County 		65 2 0
Polnell Heights Water Association
Island County 		65 3 1
Whitstran Heights Water Association
Benton County 		65 2 0
Crescent Acres Water Association
Island County 		64 2 0
Cattle Point Water District
San Juan County 		63 2 0
Campbells Glen
Island County 		62 6 1
Whidbey Highlands Water Assoc
Island County 		62 2 0
National Food NW Lind
Adams County 		61 3 0
Silver Springs Estates Comm Assn
Snohomish County 		61 1 0
Suburban Mobile Park
Island County 		60 2 0
Fall City Water Dist. (plum Creek)
King County 		59 3 0
Orcas Island Golf Estates
San Juan County 		57 3 0
Pleasant View Water Company
Island County 		57 1 0
Sleeper Acres Comm. Assoc. Inc.
Island County 		56 3 0
Mutual Materials Company
Spokane County 		55 5 0
Diablo Wtr Sys-Seattle City Light
Whatcom County 		53 3 0
Syringa Heights Mobile Home Park
Spokane County 		52 4 1
Alpine Acres Community Association
Chelan County 		51 6 0
Bonnie View Water
Island County 		50 2 0
Lyon RD Community Association
Island County 		50 1 0
Taylor Road Water System
Island County 		50 1 0
Riverside Water Dist #1
Snohomish County 		48 3 0
Camano Sunset Water System
Island County 		47 1 0
Damman School
Kittitas County 		45 5 1
Williams Lake Beach Club
Spokane County 		45 2 0
Township 29 Water Association
Island County 		42 2 0
Polnell Landing Water Assoc.
Island County 		41 4 0
Smwe Vineyard 8
Benton County 		41 1 0
Seawest Water System
Island County 		38 2 0
E.l.c. Water System
San Juan County 		36 2 0
About this data

A system is counted once if any of its violations in the past three years involved TTHM (Total Trihalomethanes), including monitoring and reporting lapses. Rules violated and status in the table are for the whole system, not TTHM (Total Trihalomethanes) alone.

Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The Washington records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.