The 1998 EU Drinking Water Directive introduces a maximum allowable lead concentration of 25 ?g/l from the end of 2003, reducing to 10 ?g/l at the end of 2013. The 25 ?g/l standard will be difficult to attain for many waters, and the 10 ?g/l will be impossible, without reducing lead solubility.

Where water comes into contact with lead in the presence of carbonates, the carbonate in the water reacts with lead forming one of several lead carbonates, mainly either lead carbonate (PbCO ₃) or basic lead carbonate (Pb ₃(CO ₂) ₂(OH) ₂). The species formed depends on pH and alkalinity. The concentration of lead carbonate in water is a minimum at a pH value of around 9-9.5. At this pH value the lead concentration is lowest in low-alkalinity waters, with a minimum lead concentration of around 25 ?g/l. ^[5] However, low-alkalinity waters have low buffering capacity and it is often difficult to maintain the pH of the water as it moves through the distribution system.

Where the water contains dissolved orthophosphate the concentrations of lead are much lower as lead phosphate compounds are formed and these are less soluble than lead carbonates. Dosing orthophosphate reduces minimum lead concentrations to around 5 ?g/l. In a low-alkalinity water the pH range required for minimum lead concentrations is 7.5 8. As alkalinity increases a pH in the range of 7.2 7.8 is required.

Thus one approach to...