The places from which water companies get their water are known as WATER SOURCES.
Water in reservoirs, seas, rivers, steams and other open water areas is known as SURFACE WATER and so a reservoir is a good example of a SURFACE WATER SOURCE.
Characteristics of Surface Water
1: Unlike ground water, surface water generally has no natural filtration system in place. Hence, it is always much dirtier than ground water as during storms the rain washes mud from the surrounding land into the water source and strong winds will cause currents in the water that disturb the fine sediments which have settled on the bottom, making the water muddy in appearance.
2: Even without the effects of storms, surface water is usually much dirtier than ground water as it is open to the elements and usually has fish, mammals, birds, and other animals living in or around it, as well as plants growing in it. These living things release their waste directly into the surface water source.
3: Owing to the fact that surface water is naturally quite dirty and is a habitat for a wide range of living things, it is inevitable that such water sources have lots of germs (bad bacteria), living in the water.
4: Surface water is open to the sun and so will be warmed up by the sun's energy. This gives rise to a number of problems:
Evaporation - As the sun shines down on the water it warms it up and the water starts to evaporate. This means that some of the precious water in surface water sources is lost to evaporation. This can become a particular problem during prolonged hot periods where the heat makes people use more water for drinking and bathing whilst evaporation helps to empty the reservoirs more quickly. This can give rise to a situation known as a DROUGHT, where there is not enough water available in the reservoirs and rivers to meet the needs of people and wildlife.
Algal Blooms - There is a group of plants known as algae that live in water. They are very small and in fact in most cases are so small that you have to use a microscope to see them. As with all plants, algae harness the energy of the sun in order to grow and reproduce. This is achieved using a chemical process called PHOTOSYNTHESIS, which is made possible by the fact that plants contain a pigment called CHLOROPHYLL. During the summer the days are longer and the sun is hotter. This combination means that there is a lot of sunlight energy available for the plants and so they flourish in the water. Sometimes the algae can flourish so well that an ALGAL BLOOM occurs, where vast numbers of algae develop very quickly. This causes problems in surface water sources in a number of ways:
a: The algae release waste into the water that make it taste and smell unpleasant, and appear slightly coloured, often a green/yellow/brown colour. These tastes, smells and colours have to be removed in the cleaning process and so they make it more expensive to clean the water and turn it into drinking water.
b: The large number of algae in the water may start to clog up the place where the water is cleaned, i.e. the water treatment works, and so parts of the water treatment works such as filters have to be cleaned more frequently, again making it more expensive to clean the water.
5: When it rains the rainwater can run off the land and into the surface water source. If it rains after farmers have put chemicals such as fertilisers or pesticides on their crops to help them grow, the chemicals used may dissolve in the rainwater and be carried into the surface water source, polluting it in the process. These pollutants are considered to be contributory factors to the development of some illnesses.
6: Owing to the fact that surface water is much dirtier than ground water, the cleaning process for surface water is much more involved and has many more stages.
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