The earliest agrarian societies depended upon rain for agriculture. Historically, rain falling in the countryside ran into creeks, streams, and rivers, and rivers rarely ran dry. Rainfall was absorbed into the ground, which served as a huge reservoir. The water that accumulated underground emerged as springs and artesian wells, or in lakes, swamps, and marshes. Most of the water that leaked into the ground cleansed itself in the weeks, months, or years it took to get back to an aquifer, which is a water-bearing rock formation.

Early towns developed near rivers for access to transportation and wells. Streets sloped to drain in the river, which ran to river basins and the sea. Later on, marshy areas were filled in and buildings were built, along with paved streets and sidewalks. Storm sewers and pumping stations were constructed to carry away the water. The rapid runoff increased the danger of flooding, and concentrated pollutants in waterways. Water ran out of the ground into overflowing storm sewers, without recharging groundwater levels.

Today, subdivisions slope from lawns at the top to street storm drains at the bottom. Once water enters a storm drain, it dumps out in rivers far away from where it started. Huge amounts of storm water also leak into sewer pipes that mix it with sewage and take it even farther away to be processed at treatment plants. The result is a suburban desert, with lawns that need watering and restricted local water supplies.

In most of the United States, the rainwater that falls on the roof of a home is of adequate quality and quantity to provide about 95 percent of indoor residential water requirements. However, a typical U.S. suburban household could not meet all its water needs with rain off the roof without modifying the members' water use habits. Rainwater can make a major contribution to the irrigation of small lawns and gardens when a rain barrel below a downspout or cisterns located above the level of the garden collect and store water for later release.

For centuries, traditional builders have incorporated rainwater into their designs. In the world's drier regions, small cisterns within the home collect rainwater to supplement unreliable public supplies. With the advent of central water and energy supplies in industrial societies, rainwater collection and use became less common. It has become easier to raise the funds (with costs spread to consumers in monthly bills) to build a water treat ment plant with the related network of pipes than to convince individuals to collect, store, and recycle their own water. An individual who chooses to use rainwater to flush toilets must pay for this private system up front, and continue to pay through taxes for municipal water treatment, so conservation can add expense.

Designing buildings to hold onto even a part of the 50 to 80 percent of rainwater that drains from many communities requires a radical rethinking of how neighborhoods are built. Recently, progress has been made in designing building sites to improve surface and ground-water qualities. The community master plan for the Coffee Creek Center, a new residential development located 50 miles southeast of Chicago, was completed in 1998 by William McDonough + Partners. Coffee Creek itself is being revived with deep-rooted native plants that build healthy and productive soil and assure biological resiliency and variety. A storm water system makes use of the native ecosystem to absorb and retain rainwater, while wastewater will be treated on site, using natural biological processes in a system of constructed wetlands.

In Bellingham, Massachusetts, workers are ripping up unnecessary asphalt to let rainwater into the ground. Concrete culverts are being replaced with tall grasses to slow runoff from parking lots. Cisterns under school roofs will catch rainwater for watering lawns. Tiny berms around a model home's lawn are designed to hold water until it is absorbed into the ground, and a basin under the driveway will catch water, filter out any motor oil, and inject the water back into the lawn.

In Foxborough, Massachusetts, the Neponset River is being liberated from under the grounds of Foxborough Stadium. The Neponset was partially buried in culverts in the late 1940s, and weeds and debris choked the remaining exposed portion. Plastic fencing and hay bales appeared to imprison the stream in an attempt to halt erosion. The river is now being freed into a 20-meter (65-ft) wide channel and wetlands corridor on the edge of the new stadium complex, creating a 915-meter (3000-ft) riverfront consisting of an acre of open water, four acres of vegetated wetland, and three acres of vegetated upland. The new 68,000-seat Gillette Stadium will use graywater to flush the toilets that football fans use on game days. Storm basins that drain into retention ponds filter out the oil, salt, and antifreeze that collect in parking areas. The project also includes a 946,000-liter (250,000-gallon) per day wastewater treatment facility and extensive use of recycled construction materials.

Acid rain, a result of air pollution in the northeastern United States, Canada, and some other parts of the world, makes some rainwater undesirable. Dust and bird droppings on collection surfaces and fungicides used for moss control can pollute the supply. Steep roofs tend to stay cleaner and collect less dirt in the rainwater.

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