Not always the proper water for human consumption and for the supply of a population is in good condition. Water may be contaminated or polluted.
Contamination = existence of living things such as microorganisms and worms causing disease. Example: Schistosomes (worm that causes schistosomiasis).
Pollution = Existence of toxic substances in excess. Example: mercury and oil.
Mercury (Hg) is a very dense and poisonous metal that prospectors use on river banks to separate gold from other particles that come along or stick to it. Oil that is discarded by ships at sea prevents plants from performing photosynthesis.
How does water get to homes?
Water is transported from springs or dams to treatment plants through very large pipes called water mains. In treatment plants, water is purified. After that, it is led to other pipes that connect to the water tanks and reservoirs that supply the city.
All cities need to have a treatment plant because the springs come with unsafe water, often contaminated or polluted.
Water treatment plants
Since water in springs can be very impurities, it must go through a treatment plant. If this water is not well treated can cause serious problems in the health of the population. Some of the general water treatment procedures are: flocculation, decantation, filtration and chlorination.
Flushing water unfit for consumption at the treatment plant. First it goes through tanks containing a solution of lime (calcium oxide, CaO) and aluminum sulphate Al2(ONLY4)3. These substances react by forming another substance which is aluminum hydroxide (Al (OH)3).
Aluminum hydroxide deposits by dragging the suspended solid impurities into the water. This procedure is the flocculation, name given due to the formation of floccule.
In the next step, the water goes to a water tank. decantation, where the particles that have formed in flocculation are denser than water and thus settle in this tank. So by this time the water is a little cleaner. The next process is to filtration, where water passes through a multilayered filter of gravel and sand and activated charcoal. As it passes through these layers, it leaves its impurities.
After all these processes, the water is not yet purified. There are still microorganisms in it. Then it must pass through a deposit containing chlorine. Chlorine (Cl) is a substance that is capable of killing the microorganisms present in water. We call this process the chlorination.
Now water is fit for consumption. It is already purified. It stays in warehouses until it is distributed to the city.
There are certain places where there is no water treatment. Others, although receiving treated water, also prefer to purify it further.
There are some methods for water purification, such as home purification (filtration, boiling, ozonation) and industrial purification (distillation).