How Is Water Made Drinkable?

First of all, why does water have to be made drinkable? Why can't we drink it just as we find it? The reason is that we can hardly ever obtain pure water. Probably, the purest natural source of water is snow.

The next purest water is rain water, but rain contains dissolved gases of the air and traces of carbon dioxide, chlorides, sulphates, nitrites and ammonia.
 
Even the water from streams and lakes that are found in the mountain may contain dissolved inorganic salt.

Water from rivers and lakes in low regions is usually quite polluted. Water from springs and wells has been filtered through the ground, so it is quite pure, but it may also contain inorganic salts.

So it seems that all water we drink need to be purified to some degree. There are many methods of doing this.
 
 One is simply by storage. When water is stored in a reservoir certain actions take place. Solid impurities settle at the bottom, a process known as sedimentation.

Many bacteria lose their power when water is kept in a storage reservoir. But this method does not give complete protection. So chemicals may be added to provide better sedimentation.
 
In addition, the water may be aerated (to allow air to act upon it) to remove tastes and odours and dissolved gases.

Many years ago it was discovered that if water could be filtered, through sand, many of the impurities and most of the bacteria could be removed.
 
So various methods for sand-filtering were set up, including a method that forced the water through mechanically at a great speed.

A commonly used method for purifying water is chlorination. This is very cheap, quick and an effective method. From two to eight pounds of chlorine are added to a million gallons of water.
 
 This is enough to destroy most of the dangerous bacteria that may be in the water.