Answer to Question 1 Store water until it is needed.
Reduce flooding hazard
Answer to Question 2Raw sewage enters the wastewater treatment system by passing first through a coarse grid that filters out the largest
pieces of solid material. The water then moves into the primary treatment facility where floating debris and suspended
particles of solid material are filtered out or allowed to settle out. During this phase, biological decomposition
of the organic material begins. The partially treated wastewater moves into the secondary treatment facility
where biological decomposition continues and chemicals that encourage coagulation of smaller particles into larger
clumps are added. The water is allowed to move very slowly, during which time further biological decomposition
takes place and coagulated particles are allowed to settle or be filtered out. By the end of the second stage, at least
90 percent of all impurities have been removed. A final filtration at the end of the secondary treatment stage removes
most of the remaining solid matter. Finally, the partially purified water receives a tertiary treatment consisting of the
introduction of chemicals designed to neutralize most of the remaining biological and chemical contaminants. One
final filtration removes most of the remaining suspended solids. Water passing out of the tertiary treatment stage is
then reintroduced into the natural water cycle.
Major reservoirs and flows of the hydrological cycle.
Hand Washing Using Soap and Water
Basic tissue types and structures of the alimentary canal.
Basic molecular mechanisms of delayed-type hypersensitivity.
The structure of liquid water
The water cycle