Water Treatment

The City of Concord distributes water throughout the community after treatment at the Water Treatment Plant. Water is collected from Penacook Lake and treated according to national standards enforced by the U.S. Environmental Protection Agency (EPA) and the Safe Drinking Water Act (SDWA). Concord General Services’ Water Treatment Division ensures these standards are met to provide the highest water quality possible and to protect public health, while still ensuring environmental protection.

Water Treatment Process

The City of Concord’s Water Treatment Plant follows a traditional treatment process of coagulation, flocculation, sedimentation, and filtration.

1. Coagulation

Raw water from Penacook Lake is screened to remove large floating debris before entering the treatment plant. The water then travels through the raw water pumps and a coagulant is added to create floc, which are sticky particles that bond with the elements in the water that need to be removed (such as sticks, twigs, leaves, natural minerals, etc.).

2. Flocculation

The water then passes through to one of four flocculation basins where the water and coagulant are first rapidly mixed, then slowly mixed to ensure clustered particles. The thicker the cluster, the easier the element can be removed from the water.

3. Sedimentation

After passing through the flocculators, the water flow slows down to allow the now heavy clustered particles to settle to the bottom of the sedimentation basin by gravity. Scrapers push the material at the bottom of the basin into a sludge drain, which travels to the City’s Wastewater Treatment Plant.

4. Filtration

Water then flows down through a 3-foot dual media filter made of silica sand and Granular Activated Carbon to ensure any remaining particulate is captured.

5. Secondary Treatment

Sodium Hypochlorite (Chlorine) is added as the primary disinfectant. The water then stays in the 4.7 million gallon clearwell to allow for necessary contact time. After this process, the water is treated for corrosion control (to reduce pipe disintegration into the water), alkalinity (to maintain water consistency), and secondary disinfection (to transition chlorine to chloramine to maintain disinfectant longer throughout the distribution system).

6. Distribution

Treated water is first transmitted to the five storage tanks throughout Concord. The tanks have a combined storage capacity of 7.5 million gallons of water. It is important to make sure these water tanks have an adequate supply of water at all times in order to maintain water distribution in emergency situations. The City of Concord also owns a well field that can provide up to 1 million gallons of ground water a day if needed as a backup to the treatment plant. After water reaches the storage tanks, distribution then continues to supply potable water throughout the whole community. The tanks are spaced out throughout the city to maximize water distribution and pressure to surrounding areas.