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Water : Distribution

   · System Description
   · Transmission System
   · Pressure Zones
   · Mains and Services
   · Storage Facilities
   · Leaks

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 renewal
  • 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 reducing valves.
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System Description

Water 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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Transmission System

Parts of the City’s 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-1970’s, 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 plant’s clear well.
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Pressure Zones

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 (PRV’s). 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 customer’s 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 delivery systems.
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Mains and Services

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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Storage Facilities

Water storage 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 meter
  • 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 line
  • Inefficient hose bib or shutoff valves
  • Holes or breaks in interior plumbing lines
  • Leakage inside plumbing fixtures (toilet fixture leaks are common)

Valve Leaks
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 others.

Miscellaneous Leaks
Breaks from excessive pressure, settlement, overloading, improper installation, improper materials, and improper operation may occur.

The City 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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