GEF

Unit 3  |  Water Use and Human Water Systems 79 Household water is drawn from a wide variety of sources, including rivers, lakes, reservoirs, and groundwater. Water from some of these sources, such as groundwater, may be relatively clean and can be used with little treatment. Many cities and municipalities, such as New York City and Boston, have upheld high water quality by protecting land around water sources. Once captured, most municipal water is piped into central treatment centers, where it is chemically clarified and filtered to remove debris and sediment. Following filtration, water is disinfected with one or several chemicals, such as ozone or a chlorine compound, in order to kill harmful bacteria or other pathogens. Water may also be further treated by adding fluo- rine, a chemical which improves dental health. Treated water may be stored in water towers or tanks, then dis- tributed via pipes and pumping stations to homes, businesses, and other buildings. After use, water enters the sewer system. Some water systems separate greywater from sinks, showers, and washing machines from blackwater from toilets. In these systems, greywater can be reused for purposes such as water- ing lawns and gardens and flushing toilets, saving high-quality water for other needs. Until the mid-twentieth century, the majority of wastewater was released untreated into water bodies, causing severe water pollution, threatening human health, and harming ecosystems through eutrophication . Since the passage of environmental legislation such as the Clean Water Act in the U.S., governments have required that wastewater be treated before being returned to the environment. Wastewater is treated in several stages, including settlement to remove solids, mechanical filtering, and biological treatment to kill patho- gens. In some wastewater facilities, water is then pumped into constructed wetlands , in which plants and other organisms further purify wastewater. Once water is sufficiently clean, it is returned to water bodies. In some cases, recycled wastewater can be reused for industrial purposes. WATER QUALITY The chemical and biological profile of water. GREYWATER Wastewater that is created in homes or buildings that can be recycled onsite for irrigation, landscaping or construction. BLACKWATER Water used to flush away human waste. WASTEWATER Water that has been used by humans. EUTROPHICATION The process in which a body of water becomes excessively enriched with nutrients resulting in growth of aquatic life and depleting the oxygen availability for other organisms. CLEAN WATER ACT A U.S. federal law that regulates the discharge of pollutants into the nation’s surface waters. CONSTRUCTED WETLANDS Artificial wetlands created for filtering wastewater and improving wildlife habitat.