**2.3 Importance of pH**

pH is the final parameter that is considered for determining quality as part of post treatment processes. The desired target pH is often determined as a by-product of the previously mentioned parameters: alkalinity and calcium content. This is due to the fact that 1) the dissolution or precipitation potential of the water with respect to calcium carbonate is often used as the key indicator to the stability of water; and 2) the alkalinity, calcium content and pH are the three major contributing factors in determining dissolution or precipitation potential of the water. As noted earlier, this calco-carbonic balance is extremely important for cement-lined or concrete infrastructure. In such circumstances, system designers often opt for a slightly

precipitative water (pH > pHsat) so that a protective scale is built up on the surface of the cement lined pipes or tanks. For other materials of construction, pH also appears to play an important role in controlling corrosion. The World Health Organization for example recommends a pH range of 6.8–7.3 to deal with iron corrosion, 8.0–8.5 to deal with lead and copper corrosion and a pH of less than 8.3 to deal with brass corrosion [13].
