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. The 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 deferred or demagnetized; 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 an 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 after use.
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