Pre-Treatment:

To reduce the load on main purification units such as sedimentation tanks, filter etc., raw water from river or streams is not pumped directly but sent to such units after pre-treatment. There are some intermediate processes, which collectively are called pre-treatment.  These involves:

(a) Screening

(b) Raw water storage

(c) Pre-chlorination

(d) Aeration

(e) Algal control

(f) Preliminary settling

Each process performs a specialized function which may be employed independently or in combination as per the need of the situation.