CBSE Class 7 Answered

Waste water can be treated to remove large impurities by the process of filtration.

Water is filtered through the layers of sand, fine gravel and medium gravel. Filtration makes the waste water clean from various types of impurities. The water is filtered continuously until it becomes clear. The filtered water is then treated with a disinfectant such as chlorine and stirred to obtain completely clear water.

At homes, water is filtered through the following equipments:

Candle filter

• Water can also be passed through a porcelain candle filter where most of the bacteria are trapped.
• Porcelain filters cannot remove viruses from water. 

Ultraviolet filter

• An ultraviolet filter can also be directly attached to the tap.
• The water which we draw from this tap passes through this filter.
• The ultraviolet light kills the germs present in water.