Utilities > Water >
Water : Distribution
· System Description
· Transmission System
· Pressure Zones
· Mains and Services
· Storage Facilities
The water distribution
system delivers potable water to approximately 13,500 metered customers. The goals of the
program are to provide uninterrupted water flow at adequate pressures, to meet all fire
and domestic flow requirements, and to minimize system water loss due to leakage. In order
to accomplish these goals, the water distribution program has seven major work objectives.
They are as follows:
- Pump station and tank maintenance
- Water main maintenance and repair
- Water service installation and service
- Fire hydrant installation
- Fire hydrant maintenance
- Cross connection control
- Underground Service Alert (USA) markouts
Because of the geographic setting of San
Luis Obispo, the water distribution system is a very complex structure of pipes, pumps, storage tanks, and pressure
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Zone Map (click
to link to pdf)
The water distribution program delivers
potable water from the water treatment plant and wells to customers and fire hydrants via
three storage reservoirs, ten pump stations, twelve storage
facilities, and approximately 150 miles of water mains. It is unlikely this basic
distribution pattern will change, since the water treatment plant will continue to be the
principal source of treated water for the City.
Growth within the City has placed
increased demands on the water distribution system. Additionally, many
pipes throughout the City are over 100 years old,
and do not provide adequate capacity to meet current fire-flow requirements. Even without
growth or fire protection requirements, aging pipes must be replaced to avoid major
service disruptions and leaks due to deterioration.
There are approximately 150 miles of
water distribution pipelines throughout the City. The engineering estimate for the life
expectancy of these facilities is 50 years. Complete replacement within the term of life
expectancy would require that the City replace an average of 2% of the system
infrastructure each year.
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Parts of the Citys water
transmission system are over 100 years old. Most of the pipes are made of cast iron. Other
pipes are made of asbestos cement (located primarily in the Laguna Lake area), or, since
the mid-1970s, PVC. Water pipes serve two basic functions. The larger pipes or
transmission mains move large volumes of water from one portion of the City to another.
They range in size from 12 inches to 30 inches. The smaller pipes or distribution mains
are to distribute water within a local area and deliver it to each property in the City.
They range in size from 2 inches (in the older portions of the City) to 12 inches. The
current minimum standard is 8 inches for distribution mains.
Water from the water treatment plant in
Stenner Canyon is transported through a 30 inch transmission line 3,500 feet to the
transfer pumps (located on Stenner Canyon Road). The transfer pumps take approximately 48%
of the water, increase the pressure, and then provide water to Stenner Canyon Reservoir,
Cal Poly, and other portions of the City, generally north and east of the Southern Pacific
Railroad tracks. From the transfer pumps, there are two 24 inch transmission lines that
move water about one mile to the city limits. One pipe is the high pressure line from the
transfer pumps and the other pipe has lower pressure supplied directly from the water
treatment plants clear well.
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The water delivered from the treatment
plant is split into two main distribution networks. About 52% flows into the City by
gravity and the other 48% is pumped to a storage reservoir at a
higher elevation and then flows into the various service areas by gravity and through
pressure reducing valves (PRVs). The most apparent strain is in the pumped delivery
system. Since electrical power for pumping water is a major expense, a goal is to develop
a system which minimizes pumping. The goal of the water supply system is to deliver water
at pressures between 40 pounds per square inch and 80 pounds per square inch at the
customers meter without using a pressure reducing valve on the pipe connecting the
water main to the meter. This pressure range will meet the needs of most irrigation
sprinklers and other uses, and provide adequate pressure for fire sprinkler systems.
Pressure zones are established in the distribution system to maintain these pressure
ranges. The City currently has 15 pressure zones divided between the gravity and pumped
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Once raw water has been converted to
drinking water, it must be delivered to the customer with its quality intact.
Additionally, it must be at a pressure that assures adequate flow from the tap. The effort
put into constructing a wide-ranging distribution system is enormous in terms of cost,
work, and disruption to the community. The elements of a distribution system (pipes,
pumping stations, valves, storage structures, and so forth ) are expected to operate over a
long time frame as they are all expensive to replace. In particular, the piping network
(placed largely below ground) is expected to have a very long service life. Replacement
and rehabilitation work is very costly and difficult. Presumably research and development
will continue in this area and new products, techniques, and new concepts in engineering
practice will help keep the network flowing smoothly.
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facilities are necessary to provide water during peak demand periods and emergency
situations such as fires. The City has ten water storage facilities, six of which are
steel storage tanks ranging in size from .07 to 4 million gallons, three concrete
facilities with a capacity of .03 to 7.5 million gallons, and one hydropneumatic station.
The combined storage capacity is 24.21 million gallons.
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Main Line Leaks
Main line leaks range from a low of 1 gpm to over 1,000 gpm. Leaks due to corrosion
usually start small but can grow very large. Splits can occur due to excessive pressure,
improper installation settlement, or overloading. Joint leaks can occur due to corrosion,
improper installation, improper materials, or overloading.
Services Line Leaks
Service line leaks range from a low of 0.5 gpm to over 15 gpm. Service line leaks are
caused by the same factors as the main line leaks.
Residential Meter Box:
Know Your Meter Box!
Leaks within the vicinity of the meter box range from a low of a fraction of a gpm to a
high of 10 gpm. Common examples include leaks due to:
- Loose spud nuts on either side of the
- Loose packing nuts
- Damaged or broken angle stops
- Broken meters
- Damaged meter gaskets
- Damaged or broken meter yokes
Residential Customer Leaks
Leaks on the residentail customer side of the meter range from a low of a fraction of a
gpm to a high of 15 gpm. Common examples include:
- Holes or breaks in the costomer service
- Inefficient hose bib or shutoff valves
- Holes or breaks in interior plumbing
- Leakage inside plumbing fixtures (toilet
fixture leaks are common)
Leaks in distribution system valves range from a low of a fraction of a gpm to a high of
500 gpm. Common examples include leaks due to loose packing and broken valves.
Leaks may start in the systems controls
such as pressure-reducing valves, pressure-sustaining valves, pressure-relife valves,and
Breaks from excessive pressure, settlement, overloading, improper installation, improper
materials, and improper operation may occur.
recognizes that there are circumstances which result in the unintended
high usage of water. If you have discovered a leak(s) and have made the necessary repairs, or have
had an unusual event that has caused higher than normal water use,
the UBAC will review your
account for a possible adjustment.
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