Water Supply

    Water for human consumption comes from one of two basic sources:

    • Water from a well to supply an individual residence, well water for rural agricultural 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.

    The Senior Engineer has lived in the Montgomery and Harris County Areas of Texas for many years and therefore the examples used in this page will reflect his experience with the water systems of these two Counties. This system was selected because it typifies many of the water systems in the United States that rely on water sources including rivers, lakes, and low-level water retention dams.


    Design Manual for water Delivery Systems

    Standard Drawings for water Delivery Systems




    The purpose of a water delivery systems is to transport potable water from its original source, through a water treatment facility and on to its ultimate consumer. The final consumer of the potable water may be a residential customer who will use it as drinking water, water for cooking, water for sanitary conditions, and other uses in a domestic environment. Water supply also is essential for business and industry to operate.

    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.

    In this part two of section one, we will examine the functional components of the water system for an incorporated area of the State of Texas. We will be 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.

    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 the City of Houston are Lake Houston, Lake Livingston and Lake Conroe. The primary holding reservoir of the City of Houston is Lake Houston. The supply water from the lake is piped over to a treatment plant that processes the water to remove impurities and adds chemicals to bring the water into compliance with the Environmental Protection Agency (EPA) regulations on clean water for drinking and commercial cooking. The purified water, or finished water, then is pumped to several different storage tanks and storage basins around the city for release into the distribution system piping network on demand for consumer use or in the case of a working fire.

    Depending on the different elevations points throughout the city, additional pumping stations are provided to maintain adequate pressure in the water system during varying periods of consumer use or emergency waster supply demand requirements. Water flows from the storage locations through the primary, secondary, and distributor mains to supply service lines to individual water consumers and lateral lines to supply fire hydrants.

    Understanding the fundamentals of a municipal water supply delivery system is essential to closely examining the many features of a water system and the many options in designing a water delivery system. A water supply system or water supply network is a system of engineered hydrologic and hydraulic components which provide water supply. A water supply system typically includes:

    • A drainage basin The map below shows the Drainage basin of the Mississippi River.

    • A raw water collection point (above or below ground) where the water accumulates, such as a lake, a river, or groundwater from an underground aquifer. Raw water may be transferred using uncovered ground-level aqueducts, covered tunnels or underground water pipes to water purification facilities.
    • Water purification facilities. Treated water is transferred using water pipes (usually underground).
    • Water storage facilities such as reservoirs, water tanks, or water towers. Smaller water systems may store the water in cisterns or pressure vessels. Tall buildings may also need to store water locally in pressure vessels in order for the water to reach the upper floors.
    • Water Pressurizing ComponentsAdditional water pressurizing components such as pumping stations may need to be situated at the outlet of underground or above ground reservoirs or cisterns (if gravity flow is impractical).
    • Distribution Network: A pipe network for distribution of water to the consumers (which may be private houses or industrial, commercial or institution establishments) and other usage points (such as fire hydrants).
    • Sewer Connection: Connections to the sewers (underground pipes, or above ground ditches in some developing countries) are generally found downstream of the water consumers, but the sewer system is considered to be a separate system, rather than part of the water supply system.

    COMPONENTS OF A WATER SUPPLY SYSTEM: A water supply system or water supply network typically includes:
    1. Water abstraction and raw water transfer
    Raw water (untreated) is collected from a surface water source (such as an intake on a lake or a river) or from a groundwater source (such as a water well drawing from an underground aquifer) within the watershed that provides the water resource. The raw water is transferred to the water purification facilities using uncovered aqueducts, covered tunnels or underground water pipes.
    2. Water Treatment
    Virtually all large systems must treat the water; a fact that is tightly regulated by global, state and federal agencies, such as the World Health Organization (WHO) or the United States Environmental Protection Agency (EPA). Water treatment must occur before the product reaches the consumer and afterwards (when it is discharged again). Water purification usually occurs close to the final delivery points to reduce pumping costs and the chances of the water becoming contaminated after treatment.
    Traditional surface water treatment plants generally consists of three steps: clarification, filtration and disinfection. Clarification refers to the separation of particles (dirt, organic matter, etc.) from the water stream. Chemical addition (i.e. alum, ferric chloride) destabilizes the particle charges and prepares them for clarification either by settling or floating out of the water stream. Sand, anthracite or activated carbon filters refine the water stream, removing smaller particulate matter. While other methods of disinfection exist, the preferred method is via chlorine addition. Chlorine effectively kills bacteria and most viruses and maintains a residual to protect the water supply through the supply network.
    3. Water distribution network
    The product, delivered to the point of consumption, is called fresh water if it receives little or no treatment, or drinking water if the treatment achieves the water quality standards required for human consumption.
    The energy that the system needs to deliver the water is called pressure. That energy is transferred to the water, therefore becoming water pressure, in a number of ways: by a pump, by gravity feed from a water source (such as a water tower) at a higher elevation, or by compressed air.
    The water is often transferred from a water reserve such as a large communal reservoir before being transported to a more pressurised reserve such as a water tower.
    In small domestic systems, the water may be pressurised by a pressure vessel or even by an underground cistern (the latter however does need additional pressurizing). This eliminates the need of a water-tower or any other heightened water reserve to supply the water pressure.
    These systems are usually owned and maintained by local governments, such as cities, or other public entities, but are occasionally operated by a commercial enterprise (see water privatization). Water supply networks are part of the master planning of communities, counties, and municipalities. Their planning and design requires the expertise of city planners and civil engineers, who must consider many factors, such as location, current demand, future growth, leakage, pressure, pipe size, pressure loss, fire fighting flows, etc. — using pipe network analysis and other tools.
    As water passes through the distribution system, the water quality can degrade by chemical reactions and biological processes. Corrosion of metal pipe materials in the distribution system can cause the release of metals into the water with undesirable aesthetic and health effects. Release of iron from unlined iron pipes can result in customer reports of “red water” at the tap . Release of copper from copper pipes can result in customer reports of “blue water” and/or a metallic taste. Release of lead can occur from the solder used to join copper pipe together or from brass fixtures. Copper and lead levels at the consumer’s tap are regulated to protect consumer health.
    Utilities will often adjust the chemistry of the water before distribution to minimize its corrosiveness. The simplest adjustment involves control of pH and alkalinity to produce a water that tends to passivate corrosion by depositing a layer of calcium carbonate. Corrosion inhibitors are often added to reduce release of metals into the water. Common corrosion inhibitors added to the water are phosphates and silicates.
    Maintenance of a biologically safe drinking water is another goal in water distribution. Typically, a chlorine based disinfectant, such as sodium hypochlorite or monochloramine is added to the water as it leaves the treatment plant. Booster stations can be placed within the distribution system to ensure that all areas of the distribution system have adequate sustained levels of disinfection.
    4. Topologies of water distribution networks
    Like electric power lines, roads, and microwave radio networks, water systems may have a loop or branch network topology, or a combination of both. The piping networks are circular or rectangular. If any one section of water distribution main fails or needs repair, that section can be isolated without disrupting all users on the network.
    Most systems are divided into zones. Factors determining the extent or size of a zone can include hydraulics, telemetry systems, history, and population density. Sometimes systems are designed for a specific area then are modified to accommodate development. Terrain affects hydraulics and some forms of telemetry. While each zone may operate as a stand-alone system, there is usually some arrangement to interconnect zones in order to manage equipment failures or system failures.
    5. Water network maintenance
    Water supply networks usually represent the majority of assets of a water utility. Systematic documentation of maintenance works using a computerized maintenance management system (CMMS) is a key to a successful operation of a water utility.