The process in a water treatment plant:
Before water is purified, it is pumped through coarse screens made of metal bars
that catches large objects like bottles and cans. The screened water is then forced into a mixing tank by the pumps.
In the mixing tank, chemical called coagulants are mixed into the water. Sticky clumps called flocs, that are aluminum hydroxide, are formed when the coagulants combine with bacteria, mud, and silt. Coagulants such as chlorine are added to kill bacteria and viruses.
As the water slowly passes into deep, broad sedimentation tanks the aluminum hydroxide settle to the bottom. They are later removed from the bottom of the tank by mechanical scrappers.
All the remaining suspended matter in the water from the sedimentation tanks is filtered through a bed of graded gravel and sand. Sand is usually spread from 61 to 91 centimeters deep in the filter basin.
A jelly-like surface mat gradually forms on the sand from contaminate. As water flows through all the bacteria, suspended matters stick to the surface mat.
The water is then forced under pressure into the air in a process called aeration. Oxygen in the air purifies the water, and gives it a improved taste and odour.
Since bacteria can sometimes get passed the purification devices, water is usually sterilized with chemical such as chlorine to ensure that it is safe to drink. At that point it only take slight amounts of chlorine to kill any bacteria.
Many municipalities add small amounts of fluorides to the water supply. This is a controversial issue because adding fluoride has a good side as well as a bad one. Adding the right amount of chloride to the water supply is safe and it reduces dental decay in children by making tooth enamel...