Plumbosolvency Control in Soft Waters

Experience of plumbosolvency control in the soft waters of north-west England is presented, and expectations for complying with the new lead standards are indicated. The influence of natural organic matter on the solubility of lead is highlighted - in particular its importance in the setting of target pH values in phosphated waters. An analysis of a large quantity of regulatory lead-compliance data confirms the benefit of the introduction of phosphate. At a distribution zone level, the impact and benefit of a change in plumbosolvency conditions on regulatory data are demonstrated using a non-parametric statistical technique. To assist in the operational management of plumbosolvency conditions, a number of performance metrics have been developed; these quantify (in a simple way), the quantity, variability and delivery of phosphate, and pH. The expected benefit from plumbosolvency control has been assessed in several ways, indicating that reasonable compliance against 25 μg/l might be achievable, but against 10 μg/l this is more questionable.