1、Unit 6 Water Supply System05.11.18lThe nature of the water source commonly determines the planning, design, and operation of the collection, purification, transmission, and distribution works.l一般说，水资源的自然状态决定了收集、净一般说，水资源的自然状态决定了收集、净化、输送和配水工程的规划、设计和运行。化、输送和配水工程的规划、设计和运行。Profession-related EnglishProfe
2、ssion-related EnglishlThe two major sources used to supply community and industrial needs are referred to as surface water and groundwater. l为社区和工业需要提供水源，两个重要的为社区和工业需要提供水源，两个重要的来源是地表水和地下水。来源是地表水和地下水。lStreams, lakes, and rivers are the surface water sources. l溪流、湖泊和河流属于地表水源。溪流、湖泊和河流属于地表水源。lGroundwate
3、r sources are those pumped from wells. l地下水是指从井里泵上来的水。地下水是指从井里泵上来的水。lFig. 2-1 depicts an extension of the water resource system to serve a small community. l图图2-1描述了向小区供描述了向小区供水的水资源系统范围。水的水资源系统范围。lThe source in each case determines the type of collection works and the type of treatment works. l水源的具体
4、情况决定了集水工程和处理工水源的具体情况决定了集水工程和处理工程的类型。程的类型。lThe pipe network in the city is called the distribution system. l城市管网叫作配水系统。城市管网叫作配水系统。lThe pipes themselves are often referred to as water mains.lwater mains 给水干管给水干管l管道本身常常称作给水干管。管道本身常常称作给水干管。lWater in the mains generally is kept at s pressure between 200
5、and 860 kilopascals (kPa).l干管中的水通常保持着干管中的水通常保持着200860千帕的压力。千帕的压力。 lExcess water produced by the treatment plant during periods of low demand (usually the nighttime hours) is held in a storage reservoir. l低需水量时期（常常是夜间），水处理厂低需水量时期（常常是夜间），水处理厂多生产的水被储存在水库中。多生产的水被储存在水库中。lThe storage reservoir may be elev
6、ated (the ubiquitous water tower), or it may be at ground level. lstorage reservoir 蓄水池蓄水池l蓄水池可以是高位的蓄水池可以是高位的(如普遍使用的水塔如普遍使用的水塔),也可也可以在地下以在地下.lThe stored water is used to meet high demand during the day. l为了满足当日的最大需水量，需要使用这部分为了满足当日的最大需水量，需要使用这部分储存水。储存水。l（As a ）Storage compensates for changes in deman
7、d and allows a smaller treatment plant to be built（主句）（主句）. l因为有储备水来适应水量供求上的变化，水厂因为有储备水来适应水量供求上的变化，水厂可以建得小一些。可以建得小一些。lStorage is also used to provide emergency backup in case of a fire. l储备水也被用来提供有火情情况下的紧急水源。储备水也被用来提供有火情情况下的紧急水源。lPopulation and water consumption patterns are the factors that govern
8、the quantity of water required and hence the source and the whole composition of the water resource system. lOne of the first steps in the selection of suitable water supply source is determining the demand that will be placed on it. The essential elements of water demand include the average daily w
9、ater consumption and the peak rate of demand. lThe average daily water consumption must be estimated for two reasons: (1) to determine the ability of the water source to meet continuing over critical periods when surface flows are low or groundwater tables are at minimum elevations; l(2) for purpose
10、s of estimating quantities of stored water that would satisfy demands during these critical periods.lThe peak demand rates must be estimated in order to determine plumbing and pipe sizing, pressure losses, and storage requirements necessary to supply sufficient water during periods of peak water dem
11、and. lMany factors influence water use for a given system. For example, the mere fact that water under pressure is available stimulates its use, often excessively, for watering lawns and gardens, for washing automobiles, for operating air-conditioning equipment, and for performing many other activit
12、ies at home and in industry. lThe following factors have been found to influence water consumption in a major way:l1.Industrial activity;l2.Meterage;l3.System management;l4.Standard of living;l5.Climate.lThe following factors also influence water consumption to a lesser degree: extent of sewerage, s
13、ystem pressure, water price, and availability of private wells. lThe influence of industry is to increase per capita water demand. Small rural and suburban communities will use less water per person than industrialized communities. Industry is probably the largest single factor influencing per capit
14、a water use.lThe second most important factor in water use is whether individual consumers have water meters. lMeterage imposes a sense of responsibility not found in unmetered residences and businesses. l This sense of responsibility reduces per capita water consumption because customers repair lea
15、ks and made more conservative water-use decisions almost regardless of price. lBecause water is so cheap, price is not much of a factor. lFollowing meterage closely is the aspect called system management.l If the water distribution system is well managed, per capita water consumption is less than if
16、 it is not well managed. lWell-managed systems are those in which the managers know when and where leaks in the water mains occur and have them repaired promptly.lIndustrial activity, meterage, and system management are more significant factors controlling water consumption than are either the stand
17、ard of living or the climate.lThe rationale for the latter two factors is straightforward. lPer capita water use increases with an increased standard of living. lHighly developed countries use much more water than the less developed nations.lLikewise, higher socioeconomic status implies greater per
18、capita water use than lower socioeconomic status. lHigher average annual temperature implies higher per capita water use, whereas areas of high rainfall experience lower water use. lThe average national value for water for water consumption in the United Stated in 1970 was 628 liters per capita per
19、day (Lpcd). lA similar study conducted in 1954 yielded a value of 556 Lpcd. lThe average single-family residence used about 208L/d. The variation in demand is normally reported as a factor of the average day. lFor metered dwellings the factors are as followings:lMaximum day = 2.2average daylPeak hour = 5.3average daylBut for large cities, the variation factors are probably between 1.21.7.
