Water - its importance and source
1.1 The importance of water
Water is one of the most important substances on earth. All plants and animals must have water to survive. If there was no water there would be no life on earth.
Fig. 6.1: Plants and animals need water.
Apart from drinking it to survive, people have many other uses for water. These include:
- washing their bodies
- washing clothes
- washing cooking and eating utensils; such as billies, saucepans, crockery and cutlery
- keeping houses and communities clean
- recreation; such as swimming pools
- keeping plants alive in gardens and parks
Water is also essential for the healthy growth of farm crops and farm stock and is used in the manufacture of many products.
Fig. 6.2: Some domestic uses of water.
It is most important that the water which people drink and use for other purposes is clean water. This means that the water must be free of germs and chemicals and be clear (not cloudy).
Water that is safe for drinking is called potable water.
Disease-causing germs and chemicals can find their way into water supplies. When this happens the water becomes polluted or contaminated and when people drink it or come in contact with it in other ways they can become very sick.
Water that is not safe to drink is said to be non-potable. Throughout history there have been many occasions when hundreds of thousands of people have died because disease-causing germs have been spread through a community by a polluted water supply.
One of the reasons this happens less frequently now is that people in many countries make sure drinking water supplies are potable. Water supplies are routinely checked for germs and chemicals which can pollute water. If the water is not safe to drink it is treated. All the action taken to make sure that drinking water is potable is called water treatment.
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1.2 Sources of water
There are many ways in which we can collect water. The main sources are discussed below.
This is water which falls to the ground as rain or hail.
This water is collected from a special area called a catchment. The catchment feeds water into a holding area via rivers, streams and creeks. The water is then stored in a natural or artificial (manmade) barrier called a dam or reservoir. Dams are usually placed at the lower end of a valley.
Catchment areas are usually far away from towns or cities to lessen the chance of the water being polluted. There are laws which control human activities, such as farming and recreation in catchment areas and on dams to make sure that water supplies are kept potable.
Fig. 6.3: A surface water dam.
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Rivers or lakes
Town or community water supplies are sometimes drawn directly from nearby rivers or lakes.
Fig. 6.4: Rivers and lakes can supply water.
These are found where underground water flows out of the ground naturally without the use of bores, wells or pumps.
Springs often occur towards the bottom of a hill or on sloping ground.
Fig. 6.5: A spring.
Rock catchment areas and rockholes
Sometimes large rocky outcrops contain low areas in which water is trapped. These low areas make good natural dams. Often a wall can be built to increase the amount of trapped water.
Fig. 6.6: A rockhole.
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Excavated dams are made by scooping out soil to make a large shallow hole. These dams are sometimes placed at the bottom of a slope to aid water collection. However, this can only be done in areas where the soil will not allow the water to drain away very easily through the ground. For example, in clay soils.
Soils which do not allow water to drain away are called impervious.
If a community wants a dam in an area where the soil is not impervious this can still be done by digging the hole and lining it with clay or an impervious liner, such as concrete or heavy plastic. Excavated dams are often used by farmers to supply water to stock.
Fig. 6.7: An excavated dam.
There is often a layer of water lying beneath the ground surface, trapped by an impervious layer of rock which will not allow it to drain away. The water may be close to ground level or it may be deep in the ground. This layer of water is called the water table.
When this water table is close to ground level the water may actually come to the surface and create a permanent wet area called a soak. This usually occurs in low lying areas or hollows.
Soaks are affected by changes in the depth of the water table. That is, if the water table drops then soaks may dry up. Some causes of this can be drought or overuse of ground water by people.
Fig. 6.8: A soak.
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The rainwater which falls on the roofs of houses is often collected using roof guttering leading through a pipe to a storage tank.
Fig. 6.9: A rainwater tank.
Note: EnHealth’s monograph ‘Guidance on use of Rainwater Tanks’ provides the most up-to-date information and advice on the range of potential hazards that can threaten rain water tank water quality. Environmental Health Practitioners are encouraged to use the guide when planning how to prevent these hazards from contaminating rainwater, straightforward monitoring and maintenance activities and, where necessary, corrective actions. The monograph can be found on the enHealth website or by using a search engine with the title of the monograph.
Bores and wells
These are holes drilled into the ground deep enough to find a permanent (long-lasting) body of water. A pipe runs down the hole into the water and a pump is used to get the water up to ground level. The water is then pumped to the community.
Fig. 6.10: A bore.
Sometimes when a bore is sunk into a low lying area the water gushes out of the hole under its own pressure. This water is under pressure because it is part of an underground body of water much of which is at a higher level than the bore opening. This kind of bore is called an artesian bore.
Fig. 6.11: An artesian bore.
A water supply taken directly from a bore or well is often called groundwater.
The water which comes from any of these sources may be salty, cloudy, smell unpleasant or have germs in it. Water of this kind would require special treatment to make it potable.