As seen in the upper part of the diagram, following in-line coagulation, 1 ppm of chlorine is required to obtain an accepltable residual chlorine level 1 km further on.

At th esecond reservoir; 7 km further on, all traces of residual cholrine have disappeared and the water is no longer potable. The cholrine has undergone a transformation and the water is now characterised by bad tatse and odours (THMs).

In the lower part of the diagram, we see the result obtained by replacing in-line coagulation by ultrafiltration :

• 10 times less chlorine at the network inlet (0.1 ppm),
• residual cholrine maintained throughout the network,
• quality of drinking water (with a residual chlorine level of 0.05 ppm),
• no formation of THMs (no bad taste.