The urban water cycle can be divided into a water supply side and a wastewater disposal side (see Figure 1-1). The basic technological framework for the water supply side began as far back as 5,000 years ago when people from the Nippur of Sumeria, a region of the Middle East, built a centralized system to deliver water into populated areas (Viessman and Hammer, 1985). The Minoans at Knossos, some 1,000 years later, improved on the concept with the installation of a system of cisterns and stone aqueducts designed to provide a continuous flow of water from the surrounding hills to dwellings in the central city. Basic concepts and instructions related to purity of water, cleanliness, and public sanitation are also recorded in the books of Leviticus and Deuteronomy (23:12-13) in the Old Testament. Talmudic public sanitation laws were enacted in Palestine to protect water quality in the centuries before and after the early Christian era ca. 200 b.c. to 400 a.d. (Barzilay et al., 1999).
The ancient Athenians were some of the first people to develop the wastewater disposal side of the urban water cycle. The Greeks moved sanitary wastes away from their central city through a system of ditches to a rural collection basin. The waste-water was then channeled through brick-lined conduits for disposal onto orchards and agricultural fields. In the ancient world, though, the Roman Empire attained the highest pinnacle for developing the knowledge and technology to select the best water supplies and to construct far-reaching networks of aqueducts to bring water supplies to Rome for distribution through pipes to wealthy homes and public fountains. The Romans also built large-scale public sanitation projects for collecting and controlling sewage and stormwater drainage. The great Roman sewer Cloaca Maxima still drains the Forum in Rome today after 2,000 years of operation.
In expanding their empire throughout North Africa and Europe, the Romans introduced the technologies needed to develop water supplies and to construct aqueducts and urban drainage systems to promote rudimentary standards of public sanitation. With the collapse of the Roman Empire, however, the public sanitation infrastructure was neglected, and the technology was lost and forgotten for a thousand years as the "Dark Ages" descended on the western world. Filth, garbage, excrement in the streets, polluted water sources, disease, plague, and high mortality rates were common consequences of the dismal public sanitary conditions that persisted well into the nineteenth century (Barzilay et al., 1999).
Throughout history, two components of the urban water cycle were often absent: wastewater treatment and the transport of treated wastewater for discharge back to natural waterbodies. For towns situated near coastal areas, estuaries, or large rivers, short-circuiting the cycle caused no immediate consequences, because these water-bodies had some capacity to assimilate raw sewage without causing water pollution problems. For many inland communities, however, water pollution problems were more acute. As populations increased, even coastal towns were forced to reckon with the consequences of ignoring the wastewater treatment component of the urban water cycle (see Rowland and Heid, 1976).
Much of the blame for incomplete urban water cycles up until the middle of the nineteenth century can be traced to a general ignorance about the consequences of allowing untreated wastewater to flow into surface waters used for drinking water downstream. As the relationship between this practice and its effects on public health became better understood, however, a community's refusal to adopt effective waste-water treatment in its cycle was more often based in politics and economics, rather than a lack of technological knowledge (see Rowland and Heid, 1976). No matter the reason, bypassing the wastewater treatment side of the urban water cycle affected both water supply and water resource users.
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