Aeration is the process on which water and air come into contact. It is carried out by spraying water in the form of spray or fountain over air. Aeration achieves the following objectives:

• It promotes good taste and removes odour by exchange between water and the atmosphere. 
• It increases the content of O₂.
• It removes CO₂, H2S and other volatile substances from water which are responsible for bad taste and odour in water. Aeration also removes impurities of Fe and Mn.

To ensure proper aeration it is necessary:

• To increase the surface area of contact of water and air. This is done by producing small droplets of water.
• The surface of the liquid should be constantly agitated to ensure proper mixing of air with water.