JWSC draws water from the
Sandy Creek Arm of Lake Travis at a location which is ideal as it is in very
deep water and the Sandy Creek Arm typically has lower suspended solids (aka.
dirt) in the water than the main body of the lake. Sodium permanganate, a
disinfectant, is added to the raw water before it reaches either treatment
At the plants, coagulants are added to help settle out solids from the
raw water before it is filtered. Chlorine is injected to this settled water
to further disinfect it through the filters. The Horton Plant has four dual
media (sand and anthracite) filters, while the Popham Plant has one tri-media
(anthracite, sand and garnet) filter.
After filtration, liquid ammonia is added to the water in order to form monochloramines
(chlorine combined with ammonia) through the clearwells of each plant and
into the distribution system. Although not as strong a disinfectant as chlorine,
monochloramine doesn’t decay as rapidly and also doesn’t react as readily
with any residual organics while out in the distribution system. This lessens
the formation of disinfection by-products which are currently regulated by
the Environmental Protection Agency.