The Waterworks Section 5.4

How does fresh water reach you? Ancient Romans built aqueducts – canals to carry water from the mountains to the city… some are still in use today

At the Waterworks When reservoirs or rivers are the source, the water must be treated Most water treatment plants occur as follows: INTAKE PRIMARY DISINFECTION CHEMICAL TREATMENT & MIXING FLOCCULATION SEDIMENTATION FILATRATION FINAL CHLORINATION

INTAKE Intake pipe is in reservoir or river and covered with a screen to prevent large objects from entering Fish and sticks stay out, but algae and other small organisms are removed during treatment

PRIMARY DISINFECTION Chlorine usually added at first to reduce the growth of algae and bacteria

CHEMICAL TREATMENT & MIXING Several of some or all of the following chemicals are added to help clean the water Alum (aluminum potassium sulfate) or iron II chloride and calcium oxide added to cause small suspended particles to stick together (called floc) Sodium hydroxide may be added to raise the pH and reduce corrosion Orthophosphate may be added to form a coating on the pipes, which prevents corrosion and leaching of lead & copper Activated carbon is added to reduce chemicals that cause taste, odor or color

FLOCCULATION After chemical treatment, water flows into a large tank with dividers or baffles As water moves, more particles stick together, and the floc grows bigger Often, large paddles slowly stir the water

SEDIMENTATION In a large storage tank, floc settles to the bottom

FILTRATION Sometimes, water is pumped to a graded sand filter with layers of rocks and sand to remove any remaining particles Graded sand filters reduce the frequency of illness due to Giardia and Cryptosporidia

FINAL CHLORINATION Chlorine is added in small amounts before the water leaves the plant In some areas, fluoride is also added to prevent tooth decay