Water treatment process
FAQs - Water Quality and Public Health
Proceso de tratamiento del agua del Departamento de Agua de Milwaukee
The Milwaukee Water Works treats Lake Michigan water at two plants using ozone disinfection and biological filtration treatment process with multiple-barrier protection.
Water Quality and Public Health
The Linnwood Water Treatment Plant has 32 filters and the capacity to treat 275 million gallons of water per day. Water for the Linnwood Plant is drawn from an intake 6,565 feet from shore, five miles north of the Milwaukee harbor, at a point where Lake Michigan is 62 feet deep. The Linnwood Plant was completed in 1939.
The Howard Avenue Water Treatment Plant has eight filters and a capacity of 105 million gallons of water per day. Its intake is 11,767 feet from shore where lake water depth is 57 feet deep. The Howard Avenue Plant was completed in 1962.
Chlorine is added to the water at the two intakes. This chlorine is a minimal dose and is used to control the growth of quagga mussels inside the crib and intake tunnel.
As source water enters the first stage of water treatment, ozone is bubbled into the water from the lake in large contactor tanks. A highly reactive gas that destroys molecules with which it makes contact, ozone destroys illness-causing microorganisms and harmful compounds. It removes taste and odor compounds in the lake water, and reduces the formation of disinfection byproducts.
At the end of primary disinfection, a quenching agent is added to remove any residual ozone. The agent reacts with ozone in water to form water and oxygen. The ozone supersaturates the water with oxygen, sometimes causing the water to look cloudy. There is an ozone destruct system should any ozone rise from the water into the air space above the water in the ozone contactor basins. There is no ozone in the water when it reaches our customers. The treatment process does not release ozone from the treatment plants into the environment.
The next step is coagulation and flocculation. Aluminum sulfate (also known as alum) and polymer are added to the water to neutralize the charge on microscopic particles in the water. The water is then gently mixed to encourage the suspended particles to stick together to form floc.
Sedimentation is the process in which the floc settles out and is removed from the water.
The next step is dual media, biologically active filtration. The water is slowly filtered through 24 inches of anthracite coal and 12 inches of crushed sand in large basins to remove very small particles.
After filtration, liquid chlorine is added as a secondary disinfectant. This provides extra protection from potentially harmful microscopic organisms.
Fluoride is added to help prevent tooth decay.
A phosphorous compound is added to help control corrosion of pipes. This helps prevent lead and copper that may be present in pipes from leaching into the water.
As the water leaves the plant, ammonia is added to change the chlorine to chloramine, a disinfectant that maintains a residual in the distribution system against bacterial contamination. Fresh, pure water is delivered to your faucets.
All chemicals that are added are certified food grade, safe for use in foods.
Treated water is stored in deep underground tanks and also flows by gravity to pumping stations and into the distribution system. The distribution system consists of 1,960 miles of water mains ranging in diameter from 4" to 60". Pumping stations and re-pumping stations help maintain adequate water pressure in the system. Reservoirs, tanks, and towers are used to store water to meet demand during peak usage.
Safe, abundant drinking water is available 24 hours a day.