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Water Supply

For more than 145 years, Lake Massabesic has served as the water supply for Manchester and portions of six surrounding communities. In order to satisfy stringent state and federal drinking water regulations, the lake water is purified at Manchester's Water Treatment Plant. The facility was completed in 1974 and has since been routinely updated with state-of-the-art equipment to improve quality control and operational efficiency and was significantly upgraded in 2006. Located adjacent to Lake Massabesic, the plant treats all of the City's water before it is pumped into a 500+ mile piping network for distribution to homes and industries.

The plant has a maximum hydraulic capacity of 50 million gallons per day and presently delivers in excess of 17 million gallons per day to approximately 160,000 consumers in the greater Manchester area. Manchester's modern treatment facility has been designed to treat a wide range of water quality problems to ensure that the customer receives the best possible drinking water.

Future Supply

Knowing that Lake Massabesic would not be sufficient to meet the demand of a large growing city indefinitely, Manchester Water Works has remained focused on short and long-term development trends, their impact on water demand, and the inevitable need for additional supply.  Water resource studies have identified and evaluated the Merrimack River as a future supply for Manchester estimating that additional source water would be needed between 2010 and 2020.  Following research and discussion with hydrogeologists specializing in large groundwater withdrawals, the concept of riverbank filtration (RBF) was brought forward as a potential means to meet future water quantity and quality goals while minimizing or eliminating the need for pretreatment.  Further investigation into the feasibility of RBF led to the design and construction of a radial collector well adjacent to the Merrimack River in Hooksett that is currently being permitted for withdrawal of just over 7 million gallons per day.  A new treatment facility near the well will purify the water to match or exceed the water quality from the Lake Massabesic plant.  The new treatment facility is estimated to be complete and serving our customers by 2020.

Drinking Water Standards

Providing our customers with tap water that meets the highest standards for both water quality and safety are our primary goals at Manchester Water Works.

Determining tap water quality is a function of sound, reliable testing.  Our laboratory at the Water Treatment Plant is certified under the most stringent national standards to perform testing on drinking water. (National Environmental Laboratory Accreditation Program - NELAP Certification)

Each week our lab performs over 500 individual tests on water being purified at our treatment facility in addition to checking on water collected from throughout our service area.  This testing is supplemented by periodic testing performed by both State run and Commercial laboratories to maintain full compliance with the Safe Drinking Water Act.  (SDWA)  Your tap water is tested at a frequency approximately four times the minimum standard, to provide greater assurance for our customers.

Please click on the link below to find results from this myriad of testing performed last year.  In addition we have provided links to both State and Federal sites that are a great source of information about the standards and regulations related to tap water.

MWW Water Quality Report

For more information about tap water quality see the EPA and DES sites.

Treatment Process Description

The Manchester Water Works operates a 50 million gallon per day (MGD) conventional water treatment facility utilizing rapid mixing, coagulation, flocculation, sedimentation, intermediate ozone disinfection, deep-bed granular activated carbon filtration, and residual disinfection processes. The treatment facility was completed in 1974 and significantly upgraded in 2006.

Lake Massabesic, located on the east side of Manchester, serves as the sole source of supply for a population of about 160,000 consumers in the greater Manchester area and portions of six surrounding communities.

Raw Water Pumping

“Raw” water from Lake Massabesic is conveyed through a 60-inch high density polyethylene pipeline intake that reaches 430 feet from the shoreline into a new, low lift pump station constructed in 1997. The original station, built in 1906 and renovated for raw water service in 1974 is maintained for redundancy. Three variable speed pumps deliver the raw water through a 48-inch pipeline to the rapid mix chambers. This pipeline is equipped with a soda ash feed point where alkalinity is boosted prior to coagulation.

Rapid Mixing

In the rapid mix chamber, the primary treatment chemical, aluminum sulfate is added to begin the process of coagulation. Two rapid mix chambers are configured in series with the capability of adding the coagulants into either or both chambers. High speed mixers ensure complete dispersion of these chemicals enabling them to react with the natural dissolved and particulate matter in the water and cause them to cluster together.


The next process, known as flocculation, involves gentle stirring of the minute particles formed in the rapid mix/coagulation process causing them to collide and stick together and form larger, denser, snow-flake-like particles called “floc”. Flow from the rapid mix chambers is distributed evenly into each of the four flocculation basins. The flocculation basins are configured in two stages separated by a baffle wall with the second stage mixers set at a slightly slower speed than the first.


The sedimentation process is achieved by allowing the water to flow slowly through a long, deep, quiescent basin that allows sufficient time for the floc particles to settle to the bottom forming sludge, a treatment process by-product. The sludge is periodically removed by isolating one of the four basins, decanting, and pumping the sludge layer to a lagoon where it is dried and moved to a landfill.

Intermediate Ozone

Settled water flows into the intermediate pump station where it is lifted into the ozone contact chambers. Ozone is a powerful oxidant and disinfectant that removes tastes and odors, along with killing or inactivating harmful organisms in the water. Ozone is generated on-site by passing a high-voltage electric current across a dielectric discharge gap through a pure oxygen stream. A combination of three, 500-pound-per-day ozone generators produces the required ozone gaseous stream that is injected into each of four ozone contact chambers through fine bubble diffusers. The contact chambers provide the necessary time for completion of the ozone reaction. Residual (excess) ozone is removed from the water by applying sodium bisulfite prior to exiting the contact chambers and continuing on to the filters.

Granular Activated Carbon Filtration

Following intermediate ozone, the water passes through one of eight deep-bed granular activated carbon (GAC) filters. Each filter contains six feet of biologically active media that completes the physical removal process. 

Hydraulic Control Structure

Combined filter effluent flows by gravity into the hydraulic control structure that provides hydraulic separation between the filters and the clearwell. The hydraulic control structure also provides an application and mixing point for post-filtration chemicals that include ammonia and sodium hypochlorite (chloramine residual disinfection), zinc orthophosphate (corrosion control), fluoride (dental protection), and sodium carbonate / soda ash (pH adjustment).

Finished Water Pumping

From the hydraulic control structure, water flows into a 700,000 gallon clearwell and finished water pumping station. A series of seven vertical turbine pumps lifts finished water into the distribution system.

Water Treatment Optimization – The Partnership for Safe Water

Manchester Water Works is committed to achieving and maintaining optimized water treatment.  In 1996, Manchester Water Works joined the Partnership for Safe Water with the goal of being recognized as one of the top water utilities in the nation. 

The Partnership for Safe Water is an alliance of the American Water Works Association, Association of Metropolitan Water Agencies, Association of State Drinking Water Administrators, United States Environmental Protection Agency, National Association of Water Companies, and the Water Research Foundation.  The Partnership's mission is to improve the quality of water delivered to customers by optimizing water system operations.  The Partnership offers self-assessment and optimization programs so that operators, managers and administrators have the tools to improve performance above and beyond even proposed regulatory levels.

The program consists of four phases:  membership application; data collection and reporting; a comprehensive self-assessment to identify performance limiting factors and apply action plans to improve future performance and water quality; and an optional Phase IV – “Excellence in Water Treatment” designation that can only be achieved by consistently meeting the most rigorous and stringent water quality goals.

On January 17, 2012 Manchester Water Works was proud to announce that its Lake Massabesic Water Treatment Plant was recognized as just the eleventh utility in the nation to receive the prestigious “Excellence in Water Treatment” award.  Further, in 2017, Manchester Water Works achieved the prestigious Phase IV “5-Year Excellence in Water Treatment Award” from the Partnership for Safe Water as one of only nine utilities to date to achieve this highly significant longevity award, honoring superior water treatment plant optimization and performance.

Our customers deserve the best water quality possible each and every day.

Contact Information

City of Manchester
Manchester Water Works
Water Supply Division

1581 Lakeshore Road
Manchester, NH

Phone: (603) 624-6482
Fax: (603) 628-6030

David Miller PE, Deputy Director - Water Supply