District Headquarters

50 Elm St., Dedham, MA 02026

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Total Trihalomethanes (TTHMs)

Since January 2022, the District has Remained in Compliance for Total Trihalomethanes

What are Total Trihalomethanes (TTHMs)?

TTHMs are a group of disinfection byproducts that form when chlorine compounds, which are used to disinfect water, react with other naturally occurring chemicals in the water. They are colorless and will evaporate out into the air. There are four significant TTHM (chloroform, bromoform, bromodichloromethane, and dibromochloromethane) potentially found in disinfected drinking water and their combined concentration is referred to as total TTHM. 

What is the District doing to keep TTHM levels in compliance?

The Dedham-Westwood Water District solicited bids for a TTHM Reduction System in Spring 2022. 

Construction for the system was completed in September 2023. Tank mixers, aerators, and vents are active at the District’s four water storage tanks. 

Our Commitment to Quality

We will continue to monitor the public drinking water supply for all regulated inorganic substances, synthetic organics, volatile organic compounds (VOCs), Total Coliform, e.coli bacteria, unregulated (secondary) substances, organic disinfection byproducts, radionuclides, as well as lead and copper. Our team is committed to providing clean, safe water. As stewards of this valuable resource, we take our job to protect public health and safety seriously. Our team of 30+ professionals work around the clock to provide reliable, cost-effective, high-quality water service that protects public health, promotes environmental stewardship, maintains customer confidence, and supports economic development and sustainability.

Recent TTHM Sampling Results

The standard for TTHMs is 80 PPB. Compliance is determined on a quarterly basis by averaging all samples collected at each location for the last 12 months, Running Annual Average (RAA).

Sample Location Quarter 1
(January - March 2023)
Quarter 2
(April - June 2023)
Quarter 3
(July-September 2023)
Quarter 4
(October - December 2023)
Dedham Medical Associates Date: January 5, 2023
PPB 59
Date: April 4, 2023
PPB 34
Date: July 6, 2023
PPB 99
Date: October 5, 2023
PPB 41
Getty Gas Station Date: January 5, 2023
PPB 59
Date: April 4, 2023
PPB 56
Date: July 6, 2023
PPB 107
Date: October 5, 2023
PPB 61
East Dedham Fire Station Date: January 5, 2023
PPB 75
Date: April 4, 2023
PPB 56
Date: July 6, 2023
PPB 87
Date: October 5, 2023
PPB 24
Far Reach Pump Station Date: January 5, 2023
PPB 88
Date: April 4, 2023
PPB 35
Date: July 6, 2023
PPB 88
Date: October 5, 2023
PPB 42
Maximum Contaminant Level (MCL) = 80 (PPB) Was OEL exceeded? NO Was MCL exceeded? NO


    • Parts Per Billion (PPB)
    • Running Annual Average (RAA): Average of one year of consecutive compliance periods, including the current one.
    • Location Running Annual Average (LRAA): RAA from the same sample location. Average of this quarter and three prior consecutive quarterly averages at the same location. 
    • Operational Evaluation Level (OEL): Average of the two previous quarter’s results and twice the current quarter’s results.

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