City of Laconia Water Department

Water Treatment Process

We have 3 filtering units in our treatment facility with each having the capability of filtering 2,000,000 gallons of water per day. We have the capacity to add 2 additional filter units for future expansion. That would give us a maximum capacity of 10,000,000 gallons per day. We are currently pumping approximately 1.5 million gallons per day.

The raw water is pumped at our office location pump room which houses our 2 raw water pumps (3,800 and 4,000 gpm). They are Variable Frequency Drives controlled. The water is pumped up to the treatment facility. The process starts by having the water pass through a static mixer where it is blended with our coagulant (alum) and our disinfection (sodium hypochlorite). The water then passes through our up flow clarifiers. The turbidity is trapped by adhering to polyethylene chips which are in the clarifier. The water then passes through our mixed media filters. The media consist of anthracite coal, silica, sand and high density silica sand. The water then settles into an 180,000 gallon baffled clearwell. Chemicals which are added to the water at that point are sodium hypochlorite (disinfection), sodium hydroxide (ph control), and sodium fluoride for dental care. The water is then pumped into our 2 million gallon storage tank. While the water is being pumped, we inject zinc orthophosphate for corrosion control. At that point the water gravity feeds to our customers in the city