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The water in a community's water mains is under pressure to offset friction and gravity as it flows through the pipes. The water pressure in public water supplies is usually at or above 345 kilopascals (kPa), which is equal to 50 lb per square in. (psi). This is also about the maximum achieved by private well systems, and is adequate pressure for buildings up to six stories high. For taller buildings, or where the water pressure is lower, water is pumped to a rooftop storage tank and distributed by gravity, a system called gravity downfeed. The water storage tank can also double as a reserve for a fire protection system.

Once the water is inside the building, its pressure ^ is changed by the size of the pipes it travels through. Bigger pipes put less pressure on the water flow, while small pipes increase the pressure. If the water rises up high in the building, gravity and friction combine to decrease the pressure. The water pressure at individual fixtures within the building may vary between 35 and 204 kPa (5-30 psi). Too much pressure causes splashing; too little produces a slow dribble. Water supply pipes are sized to use up the difference between the service pressure and the pressure required for each fixture. If the pressure is still too high, pressure reducers or regulators are installed on fixtures.

Water Quality

Whether you are working on a new building or a renovation, problems may arise with the quality of the water. Pesticides, cleaning solvents, and seepage from landfills pollute groundwater in some rural areas of the United States (Fig. 7-1). In urban areas, the level of chlorine added to prevent bacterial contamination sometimes results in bad tasting water and deterioration of pipes and plumbing fixtures.

Electric power plants discharge great amounts of waste heat into water, which can change biological and chemical conditions and threaten fish. Steel, paper, and textiles are the most polluting industries. The textile industry employs large quantities of water in fiber production and processing and in fabric finishing, especially dyeing. As a designer, you have the power to avoid products whose manufacturing includes highly toxic technologies, and to seek out ones with low environmental impact.

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