Water comes fom Long Pond, a spring-fed lake located inside a nature preserve. This isolated location protects it from contamination from outside sources, such as septic fields, agricultural pesticides and crop additives, and industrial and business waste. From a location well below the lake surface, it is pumped to the treatment plant.
Incoming water is checked for turbidity (cloudiness) to see how much organic matter is present. The small bits of organic material present are then coagulated to make them big enough to be able to be removed by filtration. After coagulation, water is filtered and the turbidity measured a second time to see how sucessful the filtration procedure was. The filtered water is then sent to be chlorinated.
Chlorine is added to the water to kill any bacteria that might be present. The goal is to add just enough chlorine to kill the bacteria and leave a little bit (residual chlorine) to kill bacteria that might have entered the distribiution pipes.
Checking for undesired by-products on chlorination
A difficulty with clorination is that it is so reactive that it combines with organic material in the water to form potentially unhealthy by-products. After chlorination, the water is checked for these by-products to ensure that their concentrations are below EPA-mandated limits.
Treated water is stored temporarily at the treatment plant and then pumped to a large standpipe at a higher altitude, from which it goes out to users.