Planning Water Quality: Potable and Subpotable Water at Selinus and Priene

Abstract

Today when the rigors of an arid climate (Arabia) or other constraints on water resources press the limits of water supply, hydraulic engineers have to reconsider the nineteenth century answer of one quality of water for all uses. In places where population density far exceeds the supply of potable water—Hong Kong—or where the scanty spring water is not enough to support the massive tourist industry—Bermuda—(Deb, 1987, 222) there is no choice but to use subpotable or nonpotable water whenever feasible. Absolute scarcity of drinking-quality water is the strongest reason for water managers today to consider alternate procedures, but in some situations the quality not quantity of water is the issue. Heavy metals, long-lasting pesticides, or other carcinogens may require separation of the purest supply for drinking and cooking from the less pure supply for other uses, lest the water itself cause disease during a lifetime of use. Since potable water amounts to a small fraction of use in a modern city—6 percent or less (J. Thapa, personal communication)—alternative delivery systems for that small amount may be feasible, with the main systems delivering subpotable water for bathing, cleaning, watering lawns, and so on, and nonpotable water for industry or irrigation. It is easier to contemplate in theory these logical divisions than to make actual plans for altering the delivery system in metropolitan water districts. Political and economic realities restrict change in built-up areas unless the danger is severe, but in some new suburbs in Florida dual pipelines are laid for potable water inside the house and subpotable outside. Drinking bottled water is becoming more common. Many municipal water systems now supply partially purified (nonpotable) water to industry for cooling or other processes. Still, these new ideas have not been widely implemented to date. It is unexpected, then, to find that the ancient Greeks had just such a triple system of water supply and reuse. Each Greek city had both public fountains and springs supplying flowing water of the best quality, and private cisterns in houses and public buildings to supply still water of good quality, plus a drain system that led used water outside the city.