AUDREY D. LEVINE UNIVERSITY OF SOUTH FLORIDA, TAMPA TA K A S H I A S A N O UNIVERSITY OF CALIFORNIA, DAVIS
Society no longer has the
luxury of using or water supplies to be sustainable, water only once. the rate at which water is withdrawn from water sources needs to be in balance with the rate of renewal or replenishment. At the same time, water quality must also be sustainable or recoverable. In nature, precipitation replenishes surface water supplies and recharges groundwater. However, urbanization, agriculture, dams and reservoirs, and other shifts in land-use patterns are altering the rate, extent, and spatial distribution of freshwater consumption and replenishment. Therefore, water withdrawn for societal needs must also be considered a source in the sustainability equation. JUNE 1, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 201A
© 2004 American Chemical Society
Annual water use
(a) The amount of water withdrawn for agriculture, industry, and municipal applications around the world has grown steadily over the past century. Reservoir water use refers to evaporation. (Adapted with permission from Ref. 3.) (b) The amount of water used for potable and nonpotable applications varies. Data from Ref. 25. (a)
Historically, after water was used for societal needs, it was labeled as sewage or wastewater and treated for discharge into receiving water or for land disposal. During most of the 20th century, wastewater treatment emphasized pollution abatement, public health protection, and prevention of environmental degradation through removal of biodegradable material, nutrients, and pathogens. However, over the past few decades, people have recognized the potential for recovering water from wastewater. In fact, in many parts of the world, using water only once is no longer an option. In this article, we summarize how water reuse has emerged as a vital component of sustainable water resources management.
Global water use (km3/year)
10,000 1000 100 10 1 Municipal Agriculture Reservoir Industry
Water usage patterns
Human society requires water for drinking, sanitation, cleaning, production of food and energy, and support of commercial and industrial activities. Figure 1a shows how water is used on a global scale. Currently, irrigation comprises about 65% of all water use; industries use about 20%; and municipalities consume another 10% (3). (To complicate matters, it is interesting to note that the volume of water evaporated from surface water impoundments [reservoirs] increased dramatically during the 20th century.) To gain insight into the major uses of water, it is important to analyze water withdrawals in relationship to the hydrologic cycle. For example, 30–90% of the water that is withdrawn for irrigation is consumed through evaporation, incorporation into crops, and transpiration. The remaining water either percolates to groundwater or is released as drainage or returns unused from the field. In contrast, most water used for municipal purposes is collected as wastewater and treated and has the potential to be reclaimed and reused. Currently, about one-third of the world’s population lives in countries that face moderate to severe water shortages. An estimated 25% of the world’s population lacks access to clean drinking water and protection from waterborne disease (4). The World Bank projected that, over the next century, the quantity of available water must increase by 25–60% to meet global needs, depending on how efficiently it is used (4). Water consumption in cities ranges from 200 to 600 liters per capita per day, depending on the standard of living, water-use efficiency, and integrity of the water transmission system (3). Water in an urban environment has characteristics that distinguish it from other commodities. First, the amount of water that urban populations consume dwarfs the quantity of all other supplies and products....