Sources of water for buildings include public water supplies, groundwater, and surface water. Each source requires careful study to determine if a sufficient quantity of safe water is available for the building being designed.
Water for human consumption, commonly called potable water, must be of suitable quality to meet local, state, and national requirements. Public water supplies generally furnish suitably treated water to a building, eliminating the need for treatment in the building. However, ground and surface waters may require treatment prior to distribution for human consumption. Useful data on water treatment are available from the American Water Works Association, Denver, Col.
Useful data on water supplies for buildings are available in the following publications: American Society of Civil Engineers, Glossary-Water and Sewer Control Engineering; E. W. Steel, Water Supply and Sewerage, McGraw-Hill Publishing Company, New York; G. Fair, J. C. Geyer, and D. A. Okun, Water and Wastewater Engineering, John Wiley & Sons, Inc., New York; and E. Nordell, Water Treatment for Industrial and Other Uses, Van Nostrand Reinhold, New York. The ASTM Manual on Industrial Water contains extensive data on processwater and steam requirements for a variety of industries. Data on water for fire protection are available from the American Insurance Association, New York, and the National Fire Protection Association (NFPA), Quincy, Mass.
Water for buildings is transmitted and distributed in pipes, which may be run underground or aboveground. Useful data on pipeline sizing and design are given in J. Church, Practical Plumbing Design Guide, and C. E. Davis and K. E.
Sorenson, Handbook of Applied Hydraulics, McGraw-Hill Publishing Company, New York. The American Insurance Association promulgates a series of publications on water storage tanks for a variety of services.
Characteristics of Water. Physical factors of major importance for raw water are temperature, turbidity, color, taste, and odor. All but temperature are characteristics to be determined in the laboratory from carefully procured samples by qualified technicians utilizing current testing methods and regulations.
Turbidity, a condition due to fine, visible material in suspension, is usually due to presence of colloidal particles. It is expressed in parts per million (ppm or mg/ L) of suspended solids. It may vary widely in discharges of relatively small streams of water. Larger streams or rivers tending to be muddy are generally muddy all the time. The objection to turbidity in potable supplies is its ready detection by the drinker. The U.S. Environmental Protection Agency (USEPA) limit is one nephelometric turbidity unit (NTU).
Color, also objectionable to the drinker, is preferably restricted to 15 color units or less. It is measured, after all suspended matter (turbidity) has been centrifuged out, by comparison with standard hues.
Tastes and odors due to organic material or volatile chemical compounds in the water should be removed completely from drinking water. But slight, or threshold, odors due to very low concentrations of these compounds are not harmful-just objectionable. Perhaps the most common source of taste and odor is decomposition of algae.
Chemical Content. Chemical constituents commonly found in raw waters intended
for potable use and measured by laboratory technicians include hardness, pH, iron, and manganese, as well as total solids. Total solids should not exceed 500 ppm. Additionally, the USEPA is continually developing, proposing, and adopting new drinking water regulations as mandated by the Safe Drinking Water Act.
Hardness, measured as calcium carbonate, may be objectionable in laundries with as little as 150 ppm of CaCO3 present. But use of synthetic detergents decreases its significance and makes even much harder waters acceptable for domestic uses. Hardness is of concern, however, in waters to be used for boiler feed, where boiler scale must be avoided. Here, 150 ppm would be too much hardness and the water would require softening (treatment for decrease in hardness).
Hydrogen-ion concentration of water, commonly called pH, can be a real factor in corrosion and encrustation of pipe and in destruction of cooling towers. A pH under 7 indicates acidity; over 7 indicates alkalinity; 7 is neutral. Tests using color can measure pH to the nearest tenth, which is of sufficient accuracy. Iron and manganese when present in more than 0.3-ppm concentrations may discolor laundry and plumbing. Their presence and concentration should be determined.
More than 0.2 ppm is objectionable for most industrial uses.
Organic Content. Bacteriological tests of water must be made on carefully taken
and transported samples. A standard sample is five portions of 10 cm3, each sample a different dilution of the water tested. A state-certified laboratory will use approved standard methods for analyses.
Organisms other than bacteria, such as plankton (free-floating) and algae, can in extreme cases be important factors in design of water treatment systems; therefore, biological analyses are significant. Microscopic life and animal and vegetable matter can be readily identified under a high-powered microscope.
Maintenance of Quality. It is not sufficient that potable water just be delivered to a building. The quality of the water must be maintained while the water is being conveyed within the building to the point of use. Hence, the potable-water distribution system must be properly designed to prevent contamination.
No cross connections may be made between this system and any portion of the wastewater-removal system. Furthermore, the potable-water distribution system should be completely isolated from parts of plumbing fixtures or other devices that might contaminate the water. Backflow preventers or air gaps may be used to prevent backflow or back siphonage. Many states or municipal water systems now have regulations which require that backflow prevention devices be installed at the building potable and fire system services. These devices are required to protect the municipal water systems from contamination. All backflow prevention devices are required to have annual inspection, testings and certification.
Backflow is the flow of liquid into the distribution piping system from any source other than the intended water-supply source, such as a public water main.
Back siphonage is the suction of liquid back into the distribution piping system because of a siphonage action being applied to the distribution pipe system. The type of backflow preventer to use depends on the type of reverse flow expected (backflow or back siphonage) and the severity of the hazard. In general, double check-valve-type backflow preventers are normally approved for low-hazard backflow conditions and vacuum breakers are approved for low-hazard back-siphonage conditions. Where the hazard is great, reduced-pressure principal backflow preventers are normally required. The local code authorities should be consulted about local and state regulations pertaining to backflow prevention.