You have studied the properties of water in Key Plumbing Principles, so there is no need to go over it again here, but understanding the properties of water will help you to appreciate why systems are designed the way they are, as well as some of the problems that can occur in systems, for example when water freezes or when limescale deposits are formed when water containing calcium carbonate is heated above 65-70℃
The water that finds its way to our taps is derived from rainfall. Rain water finds its way into rivers, lakes and the sea, where it evaporates forming water vapour and eventually falls as rain again. This continuous succession of events is known as the Water Cycle-more discussion about this can be found later in the unit.
Rain water is relatively pure, but because water is a natural solvent it can dissolve gases in the atmosphere and solids in the ground to form solutions. This means that by the time it eventually reaches natural storage areas, such as reservoirs and lakes, it is unlikely to be pure because it has picked up impurities from either the atmosphere or the ground enroute.
We mentioned earlier that water is sourced from rainfall. The continuous process of water evaporating and condensing from and to earth is called the rain cycle.
The water cycle
Water evaporates from rivers, lakes, the sea and the ground and forms clouds. Clouds contain water vapour which, under suitable climatic conditions condense and fall as rain, as shown in Figure5.3
When rain falls to the ground, some of it flows into streams, river, and lakes, the remainder soaks into the ground, where it collects temporarily and eventually evaporates.
The rain water also percolates through the ground, forming natural springs or water pockets and are referred to as underground sources.
Water Suppliers usually obtain their water for pubic consumption from two main sources:
Surface sources such as: Upland surface water, Rivers and streams.
Underground sources such as: wells, artesian wells, springs.
Water from these sources cannot be supplied directly to the consumer as they are likely to be contaminated, river water being a good example. It is vital that the water is treated first, and that also is the job of the water supplier.
The treatment of water is dependent on where it is sourced from and what impurities it contains.
Water that is sourced from springs and wells is naturally purified, and should need little disinfection.
The quality of water that is sourced from reservoirs or rivers (raw water) will determine the level of treatment. Usually this will involve several stages of treatment including settling, filtering and final polishing with activated carbon grains to remove minute traces of impurities and improve water taste.
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