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EHS 415
PUBLIC UTILITIES AND ENVIRONMENTAL HEALTH
ISSUES
`
WATER SUPPLY
AND
DISTRIBUTION
`
Water for human
consumption comes from one
of two basic sources:
`
`
Water from a well to supply an individual residence, well
water for farmstead properties, and well water for small public sector properties
that include schools, public buildings, and small
commercial enterprises.
`
`
Municipal water systems that provide potable water to a wide array of commercial
property and domestic use buildings including
apartments, condominiums, duplex housing, and single
family dwellings.
`
A “WATER SYSTEM”
HAS TWO PRIMARYREQUIREMENTS:
`
1:
First, it needs to deliver
ADEQUATE amounts of water
to meet consumer
consumption
requirements plus
needed flow
requirements.
`
2:
The water system needs to
be RELIABLE; the required
amount of water needs to
be available 24 hours a
day, 365 days a year.
`
Every municipal water system has to have a water supply source that is both adequate and reliable for
the city to be served.
`
`
`
Step 1: Screening
Water passes through a series of screens designed to remove debris such as twigs,
leaves, paper, stones, and other foreign matter.
`
Screens are frequently removed for cleaning or are back-washed from
high-pressure pumps to prevent clogging.
`
Step 2: Pre-sedimentation
While the water moves slowly through each
reservoir, much of the sand and silt settles to the
bottom.
`
Step 2: Pre-sedimentation
Treatment lines and basins are shut down periodically during times of minimum domestic consumption for
cleaning.
`
Step 3: Coagulation
A coagulant, aluminum sulfate, is added to the water as it flows to
sedimentation basins. Coagulants aid in the removal of suspended particles in the water by causing them to consolidate and settle.
`
Step 4: Flocculation
The water is gently stirred with large paddles to
distribute the coagulant. This takes approximately
25 minutes.
`
Step 5: Sedimentation
The water flows into sedimentation basins where
particles settle to the bottom. After about 4 hours, roughly 85
percent of the suspended material settles out.
`
Step 6: Filtration
Water at the top of the basins flow to large gravity filters,
traveling through layers of small pieces of hard coal, sand, and gravel. The filters help remove
smaller particles from the water.
`
Step 7: Disinfection
This may be accomplished by these methods:
~ Chlorine is added to kill bacteria and viruses.
~ Ammonia also is added.
~ The chlorine and ammonia combine to form chloramines compounds.
`
Step 8: Additives
Depending on the quality of the water at this point, the following additives may be
injected into the water stream to accomplish the stated
benefits:
`
Step 8: Additives
~ Fluoride is added to reduce tooth decay.
~ Calcium hydroxide is added to reduce corrosion in the pipes and equipment of the distribution system.
`
Step 8: Additives
Two other additives have been introduced into the
water supply before it enters the water
distribution system:
`
1.
Chloramines were added recently as a secondary
disinfectant because they were considered to be more stable
and persistent compared to the chlorine alone.
`
1.
Chloramines produce lower levels of trihalomethanes, a suspected carcinogen that forms when chlorine mixes
with the natural organic substances in water.
`
1.
Chloramines also are favored because the have a longer use expectancy time
in the water supply without settling out.
`
2.
Some countries have experienced a severe problem of excessive traces of lead in the finished water from old
lead-lined pipes in portions of their cities.
`
2.
To counteract this problem, orthophosphates have
been added to the drinking water to reduce the lead
level.
`
2.
Orthophosphates form a protective coating on pipes to prevent lead from leaching into the
water.
QUALITY OF WATER
`
Water must be treated or purified to meet
Regulatory Requirements established by the EPA .
THE REQUIREMENTS ARE DIVIDED INTO 2 CATEGORIES:
`
a.
Residential communities with populations not exceeding 3,000
`
b.
Combined residential and commercial
communities that serve a population demand
over 3,000.
`
QUANTITY OF
WATER
`
The quantity of water must be adequate to meet consumer consumption and fire-flow demands at any time of the
day, day of week, and week of the year.
`
Maintaining a continuous or uninterrupted supply of water for
municipal demands is a major challenge to many municipalities
because of the following conditions:
`Droughts
`
Growing demands that cannot be met by the treatment
plant;
`
Lack of adequate storage capacity;
`
Other communities drawing water from the
same supply sources such as a lake or a river;
`
A major commercial fire or wild land/urban interface fire that
exhausts the water supply
`
Undetected underground leakage
on the pipe distribution system.
`