1
Introduction to Water Systems
The right to water is an implicit part of the right to an adequate standard of living and the right to the highest attainable standard of physical and mental health, both of which are protected by the United Nations' International Covenant on Economic, Social and Cultural Rights, which was established in 1976. However, some countries continue to deny the legitimacy of this right. In light of this fact and because of the widespread noncompliance of states with their obligations regarding the right to water, the United Nations' Committee on Economic, Social and Cultural Rights confirmed and further defined the right to water in its General Comment No. 15 in 2002. The comment clearly states that water is indispensable for an adequate standard of living and is one of the most fundamental conditions for survival:
The human right to water entitles everyone to sufficient, safe, acceptable, physically accessible and affordable water for personal and domestic uses. An adequate amount of safe water is necessary to prevent death from dehydration, reduce the risk of water-related disease and provide for consumption, cooking, personal and domestic hygienic requirements.
According to the World Health Organization (WHO), 1.1 billion people (17% of the global population) lack access to safe drinking water, meaning that they have to revert to unprotected wells or springs, canals, lakes, or rivers to fetch water; 2.6 billion people lack adequate sanitation; and 1.8 million people die every year from diarrheal diseases, including 90% of children under age 5. This situation is no longer bearable. To meet the WHO's Water for Life Decade (2005-2015), an additional 260,000 people per day need to gain access to improved water sources.
In 2004 about 3.5 billion people worldwide (54% of the global population) had access to piped water supply through house connections. Another 1.3 billion (20%) had access to safe water through other means than house connections, including standpipes, "water kiosks," protected springs, and protected wells.
In the United States 95% of the population that is served by community water systems receives drinking water that meets all applicable health-based drinking water standards through effective treatment and source water protection. In 2007, approximately 156,000 US public drinking water systems served more than 306 million people. Each of these systems regularly supplied drinking water to at least 25 people or 15 service connections. Beyond their common purpose, the 156,000 systems vary widely. Table 1.1 groups water systems into categories that show their similarities and differences. For example, the table shows that most people in the United States (286 million) get their water from a community water system. Of the approximately 52,000 community water systems, only 8% of those systems (4048) serve 82% of the people.
Water is used in population centers for many purposes: (a) for drinking and culinary uses; (b) for washing, bathing, and laundering; (c) for cleaning windows, walls, and floors; (d) for heating and air conditioning; (e) for watering lawns and gardens; (f) for sprinkling and cleaning streets; (g) for filling swimming and wading pools; (h) for display in fountains and cascades; (i) for producing hydraulic and steam power; (j) for employment in numerous and varied industrial processes; (k) for protecting life and property against fire; and (l) for removing offensive and potentially dangerous wastes from households, commercial establishments, and industries. To provide for these varying uses, which total about 100 gallons per capita per day (gpcd) or 378 liters per capita per day (Lpcd) in average North American residential communities and 150 gpcd (568 Lpcd) or more in large industrial cities, the supply of water must be satisfactory in quality and adequate in quantity, readily available to the user, relatively cheap, and easily disposed of after it has served its many purposes. Necessary engineering works are waterworks, or water supply systems, and wastewater works, or wastewater management systems.
Table 1.1 US Public Water Systems Size by Population Served in 2007
Source: Courtesy U.S. Environmental Protection Agency.
Water System Very Small
(500 or less) Small
(501-3300) Medium
(3301-10,000) Large
(10,001-100,000) Very Large
(>100,000) Total Community water system
a No. of systems 29,282 13,906 4822 3702 398 52,110 Population served 4,857,007 19,848,329 27,942,486 105,195,727 128,607,655 286,451,204 Percentage of systems 56% 27% 9% 7% 1% 100% Percentage of population 2% 7% 10% 37% 45% 100% Nontransient noncommunity
water system
b No. of systems 16,034 2662 120 22 1 18,839 Population served 2,247,556 2,710,330 639,561 533,845 203,000 6,334,292 Percentage of systems 85% 14% 1% 0% 0% 100% Percentage of population 35% 43% 10% 8% 3% 100% Transient noncommunity
water system
c No. of systems 81,873 2751 102 15 3 84,744 Population served 7,230,344 2,681,373 546,481 424,662 2,869,000 13,751,860 Percentage of systems 97% 3% 0% 0% 0% 100% Percentage of population 53% 19% 4% 3% 21% 100% Total no. of systems 127,189 19,319 5044 3739 402 155,693
a Community water system: a public water system that supplies water to the same population year-round.
b Nontransient noncommunity water system: a public water system that regularly supplies water to at least 25 of the same people at least 6 months per year, but not year-round. Some examples are schools, factories, office buildings, and hospitals that have their own water systems.
c Transient noncommunity water system: a public water system that provides water in a place such as a gas station or campground where people do not remain for long periods of time.
Waterworks withdraw water from natural sources of supply, purify it if necessary, and deliver it to the consumer. Wastewater works collect the spent water of the community-about 70% of the water supplied-together with varying amounts of entering ground and surface waters. The collected wastewaters are treated and reused or discharged, usually into a natural water body (more rarely onto land). Often the receiving body of water continues to serve also as a source of important water supplies for many purposes. It is this multiple use of natural waters that creates the most impelling reasons for sound water quality management.
1.1 Components of Water Systems
Each section of this chapter offers, in a sense, a preview of matters discussed at length in later parts of this book. There they are dealt with as isolated topics to be mastered in detail. Here they appear in sequence as parts of the whole so that their general purpose and significance in the scheme of things may be understood and may give a reason for closer study.
Municipal water systems generally comprise (a) collection works, (b) purification works, (c) transmission works, and (d) distribution works. The relative functions and positions of these components in a surface water supply are sketched in Fig. 1.1. Collection works either tap a source continuously adequate in volume for present and reasonable future demands or convert an intermittently insufficient source into a continuously adequate supply. To ensure adequacy, seasonal and, in large developments, even annual surpluses must be stored for use in times of insufficiency. When the quality of the water collected is not satisfactory, purification works are introduced to render it suitable for the purposes it must serve: Contaminated water is disinfected, aesthetically displeasing water made attractive and palatable, water containing iron or manganese deferrized or demanganized, corrosive water deactivated, and hard water softened. Transmission works convey the collected and purified supply to the community, where distribution works dispense it to consumers in wanted volume at adequate pressure. Ordinarily, the water delivered is metered so that an equitable charge can be made for its use and, often, also for its disposal...
