The quantity of water present on the heart is constant. It evaporated from the sea and form clouds. These clouds shed water in the form of rain or snow and the water flows to the sea again. This is called the water cycle.
The domestic water supply comes from rivers and it contains available quantity of minerals, the type of mineral dissolved in it depends in the rocks over which it passed, the sources are:
Rain water: it’s not very good as drinking water, and it contains impurities and it hasn’t got many minerals;
Surface water: our many supply, but it has to be heated with a small amount of chlorine to help kill bacteria, before it can be used as drinking water;
Underground water: are usually cooler, cleaner and purer than surface water. Pollution is a very big problem, most people in third world countries use impure water and bad sanitation.

In industrialized countries factories are not allowed to a lease waste, into rivers, the main pollution agents are: harmful bacteria, industrial waste, pollution from agriculture, turbid water, algae, dead organic matter chlorine.
Recycled water: sewages plants are used to treat sewages. Water from drains are heated chemically and filtered with many filter beds. It’s the same process as that of a septic tannic not connected to a municipal drains system.
Hard and soft water: we cannot find pure water in nature because there are always traces of substances. Only distilled water doesn’t contain impurities. Hard water contains many calcium and magnesium compounds.
There are 2 types of hard water: permanent hardness is when the water is full of calcium and magnesium phosphate, which can only be removed by using an exchanged column. This column is filled with a resin which contains sodium ions, when the water posses in this column, calcium and magnesium ions are exchanged for sodium ions.
Temporary hardness water contains calcium bicarbonate that can be removed by boiling.
Hard water causes many problem, but is better for braining beer and helps to supply the body with calcium.
Soft water came from areas where there are sandstone and granite.
Mineral water (passing through soil and rocks) have absorbed beneficial salt and gases. They are use as drinking waters or they can have therapeutic effects when comes from hot springs.
Drinking water are always analyses to reveal their purity, and their beneficial substances are listed on the label of the bottle.
The industry uses large quantities of water for cooling, as a reserve of energy in the power industry, or water may be an essential ingredient, in the product itself. That’s why manufacturing plants are always placed near the water reserves.

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