Water Systems Design Considerations

In the design and construction of community water systems, economics are extremely important. This dictates that the source of supply should be selected so that little maintenance for the operational factors will be required to furnish an adequate supply of water to the community. Even though surface water supplies such as lakes and rivers, with proper treatments, are by far the more suitable from the standpoint of adequacy, the use of surface water supply systems is confined to municipalities that have a water demand in excess of 75,000 gallons per day domestic consumption to be economically feasible.

This translates to a community of about 300 residents with 12 commercial establishments, but with no manufacturing, and the ability to supply a fire flow of 500 gallons per minute (gpm) for 2 hours. This also means that ground water sources are suitable only for quite small communities typically found in more rural areas of the country. There is an important exception to the above conclusions that ground water sources typically are limited to the very small communities. This assumes that a well site or a few well sites use well pumps to supply water directly into the distribution system after water treatment.

Ground water sources can be used to pump water directly into holding basins, small reservoirs, ground-level storage tanks, or even elevated storage tanks where the amount of treated water in storage governs both the population served and the available water supply for fire protection.

A southern city, which shall remain nameless, with a population of approximately 75,000 obtains all its water from well sites and then pumps this water into storage which then supplies the distribution system upon demand. However, the price per thousand gallons of finished water is substantially higher than where surface water is used as a community water supply.

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Anatomy of a Water System

The purpose of municipal water delivery systems is to transport potable water from a water treatment facility to residential consumers, for use as drinking water, water for cooking, water for sanitary conditions, and other water use in a domestic environment.

Water supply also is essential for business and industry to operate in a municipal environment. Of no less importance is the need to supply water to properly located fire hydrants to provide the public with an effective level of fire protection. Municipal water systems also may need to provide water for special services that include street cleaning, the selling of water to contractors for erecting buildings, parks and recreation, and miscellaneous uses.

A water system has two primary requirements: First, it needs to deliver adequate amounts of water to meet consumer consumption requirements plus needed fire flow requirements. Second, the water system needs to be reliable; the required amount of water needs to be available 24 hours a day, 365 days a year. Anatomy may be defined as “separating or dividing a function into parts for detailed examination.”

A water supply system is analogous to the human circulatory system. The heart pumps blood through the arteries, veins, and capillaries to supply oxygen to all part of the body. A water pump supplies water through primary, secondary, and distributor water mains to supply water to consumers and for fire protection. This section examines the functional components of the water system by tracking the water from the sources that feed the municipal water system to the water tap.

The term tap is used in a generic sense to mean any reference point on the water distribution piping where a connection or tap is made to supply a lateral pipe to a domestic connection, a commercial connection, or a lateral line to a fire hydrant. Washington, DC, has a very old water system that has been updated in many ways. It serves as an excellent example of a basic municipal water supply system.

Variations to this system are reviewed later in this manual. Every municipal water system has to have a water supply source that is both adequate and reliable for the city to be served. The primary water source of water for Washington, DC, is the Potomac River. With minor exceptions due to ice jams and flooding, this water supply has been reliable since before the Civil War.

Water is fed to the city from intakes at Great Falls and Little Falls both by a gravity aqueduct and by a more modern pumping station. The aqueduct water serves residents of the District of Columbia, Arlington County, Virginia, and Falls Church, Virginia.

A municipal water supply system cannot service its customers unless there is a continuous supply of water to meet domestic consumption needs in the broadest sense and water needs for structural fire protection. Water sources need to be selected carefully to make sure that this fundamental requirement is met.

Two main factors that affect water supply selection are:

Quality of water: Water must be treated or purified to meet Regulatory Requirements established by the EPA (United States Government). The requirements are divided into 2 categories: a. residential communities with populations not exceeding 3,000; and b. combined residential and commercial communities that serve a population demand over 3,000. Water quality standards are covered in Chapter 3. 2) Quantity of water: The quantity of water must be adequate to meet consumer consumption and fireflow 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: S droughts; S growing demands that cannot be met by the treatment plant; S lack of adequate storage capacity; S other communities drawing water from the same supply sources such as a lake or a river; S a major commercial fire or wild land/urban interface fire that exhausts the water supply; and S undetected underground leakage on the pipe distribution system. A municipality must recognize that the quantity of available water needs to be such that maximum daily consumption demands are satisfied at all times, even during periods of drought or after years of community growth. The water delivery system needs to expand as the municipality expands.

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PVC vs CPVC

Despite the crunch in the real estate industry these past few years, the demand for cost-effective, reliable and high-quality piping and plumbing systems have increased. This is especially true a decade or so ago, when the housing and commercial building sector experienced a boom. Today, if you are in the process of having your plumbing fixed, or if a new home or office construction is in the works, you will definitely require an excellent material to use for the piping system.

Two options that you have, include PVC and CPVC pipes. Is one better than the other? Let’s try to discover the answer to that by making a comparison of the two materials. Firstly, there are the classic and popularly-known PVC pipes. The name stands for Polyvinyl Chloride, and it is a type of thermoplastic polymer, which is considered as the third most widely-produced plastic in the world.

The good thing about using the classic PVC material for piping systems, is that they are not only cheap, but they are also durable and easy to assemble. If a plumber needs the pipe to go through curves or unusually shaped openings, PVC can be made softer, and more flexible, by adding plasticizers.

So what’s the difference between PVC and CPVC? The latter stands for Chlorinated Polyvinyl Chloride, which is a type of thermoplastic material produced by subjecting PVC resin to a chlorination process. CPCV pipes are typically used for hot and cold water pipes, as well as the liquid heating system in industrial establishments.

In terms of the benefits, CPVC pipes are most suitable for carrying drinking water. Due to its smooth internal surface, CPVC pipes can be used to carry water for long distances without worrying about pressure loss, pitting or scaling. This type of pipe is also energy efficient, as it performs excellently under tough conditions, and is very easy to handle and install.

Meanwhile, PVC pipes are resistant to fracturing, they are not harmed by acids, they offer better water quality, and can even be used for thermal resisting applications. Depending on your budget and preferences, you can use either PVC or CPVC pipes for your home or office plumbing needs, but it is best to consult a professional who knows which one will suit your needs the best.

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