Important Information about your Drinking Water - Updated 5-22-17




Customers of the Holliston Water Department,

The Holliston Water Department resampled for Disinfection-by-Products on May 11, 2017 at the Rockland Street sample location where Q3, 2017 exceedances occurred.  Results for TTHM’s were 58.2 ppb (parts per billion). The maximum contaminant level (MCL) is 80 ppb. Results for HAA5’s were 23.1 ppb the MCL is 60 ppb.

The re-sampled location reflects reductions in Disinfection by Products and are below MCL (Maximum Contaminant Level) Standards.

As part of our normal drinking water monitoring the four MASSDEP approved sample sites will be sampled  in the month of June for TTHM’s and HAA5’s, both the sample results from May 11, 2017 and the June 2017 sample results will be used for the LRAA (locational running annual  average) as required by MASSDEP.

Please reference the MASSDEP Public Notification and Question and Answer guide mailed to you for additional questions or call the Water Office at 508-429-0603.


Thank You




Holliston DBP Announcement

TTHM & HAAS Question and Answer Guide


To all customers of the Holliston Water Department located in Holliston, Massachusetts

Total Trihalomethanes (TTHMs) and Haloacetic Acids (HAA5s) are Above Drinking Water Standards.

This notice is to advise our customers that our water system is in noncompliance with the drinking water standards for Total Trihalomenthanes (TTHMs) and Haloacetic Acids (HAA5s).  Although this is not an emergency, as our customers, you have a right to know what happened, what you should do, and what we are doing to correct this situation.

We are required to monitor the drinking water on a quarterly basis (every three months) for TTHM and HAA5 levels at four MassDEP approved sample sites. Results received on April 10, 2017, from samples collected during the first quarter of 2017 at the Rockland St. sample location, show that our system exceeded the standard or maximum contaminant level (MCL) for TTHMs, which is 80 parts per billion (ppb), and the MCL for HAA5, which is 60 ppb. Compliance with MCLs for TTHMs and HAA5s are calculated based on a locational running annual average (LRAA) of samples collected during the last four quarters (an average of the results found at each location over the past year).  The LRAA levels for TTHMs and HAA5s at the Rockland St. sample location reported during this period were 88 ppb for TTHMs and 65 ppb for HAA5s, which are both over the MCLs of 80 ppb and 60 ppb, respectively.

What does this mean?

This is not an immediate risk.  If it had been, you would have been notified right away.  However, pregnant women, infants, and women of childbearing age may be at increased risk and should seek advice from their health care providers if they have any concerns.  Some people who drink water containing (TTHMs) trihalomethanes in excess of the MCL over many years may experience problems with their liver, kidneys, or central nervous system, and may have an increased risk of getting cancer.  Some people who drink water containing (HAA5s) haloacetic acids in excess of the MCL over many years may have an increased risk of getting cancer.

A question and answer document on health effects, precautions, and water treatment options for TTHMs and HAA5s has been provided by MassDEP and is available on our website.  You can also contact the US EPA Safe Drinking Water Hot Line at #1-800-426-4791.

What happened?  What is being done?

TTHMs and HAA5s are a byproduct of chlorine disinfection which forms when chlorine combines with natural organic matter sometimes found in ground water supplies.  Levels of TTHMs and HAA5s can vary depending on a number of factors including the amount of chlorine used, amount of organic plant material in water sources, temperature, and seasons.  We must control TTHM and HAA5 levels while also maintaining appropriate levels of disinfectant in the water necessary to operate the water treatment plants and avoid bacterial issues.  The following actions to resolve the problem are underway.

  • The entire water system has been flushed in an effort to reduce the levels of TTHMs and HAA5s in the water mains.
  • Holliston Water Department has installed new equipment to allow for continuous system flushing. 
  • Additional sampling is being done to validate effectiveness of the flushing. 
  • Our water system is working with MassDEP to evaluate other long term solutions.

For more information please visit our website at or contact Sean M. Reese, Public Works Director, at 508-429-0603 or Holliston Water Department, 703 Washington Street, Holliston, MA 01746.

Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in apartments, nursing homes, schools, and businesses). You can do this by posting this notice in a public place or distributing copies by hand or mail.

This notice is being sent to you by The Holliston Water Dept.           PWS ID#: 2136000         Date distributed: Monday 5/8/2017