Water is filtered through a clean sand-bed and gravels. In this way light suspended particles and some germs are removed.
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Filtration and boiling: Water immediate domestic use purified in this way.
Impure water is filtered through layers of sand and gravel. Filtration may remove floating and suspended impurities but not soluble impurities and all the germs. Color and smell of dirty water does not change even after filtration.
To make this water germ-free, boil it. Boiling for 10 minutes kill most germs. Cool it.
If the water is taken from a clean deep well., it many only be treated with very small amounts of a chemical like potassium permanganate, bleaching powder or chlorine tablet.
Boiled or chemically treated water should again be filtered through muslin cloth and stored in clean container with lid.
City water supply: water from river, dam or lake is collected in large open tanks. It is allowed to stand for a few days. Heaver suspended particles of impurities settle down at the bottom. This process is called as sedimentation. Chemicals like alum may be used to speed up sedimentation. Sunlight and oxygen of the air also kill many germs.
The clear water at the top transferred to a filter-bed. This process is called decantation. Water is filtered through a clean sand-bed and gravels. In this way light suspended particles and some germs are removed.
Water is mixed with a very small amount of chlorine gas to kill all the germs. This process is called chlorination disinfection.
Sea water has lot f soluble impurities which are removed by treatment by treatment by with chemicals like zeolite.
To remove soluble impurities from water, water is distilled. Boiling of water into water vapors and then condensing the vapors back into water is called distillation. Water obtained after distillation is called distilled water.
Distilled water is the purest form of water. No germs or impurities exist in it. That is why it used in medicines.
Distilled water is not used for drinking as it contains no chemicals. Along with impurities the useful minerals has also been removed from it.