More than 100 groundwater sources operated by Anglian Water Services are vulnerable to diffuse and point pollution, and 33 of these sources have nitrate concentrations in excess of 50 mg l −1 as NO 3 . Most time series nitrate data ‘recess’ to a long-term rising baseline, upon which seasonal variations and/or data scatter are superimposed. Investigations at boreholes abstracting from the Chalk aquifer show that concentrations decrease with depth below the water table and with time after pump start-up. Abstraction rates do not affect concentrations but the combination of boreholes in use does. A reliable and robust semi-quantitative method for predicting future nitrate concentrations has been developed. Use of this method has allowed a rigorous definition of capital investment requirements under the AMP4 process to maintain compliance with drinking water standards. The method has been used to predict short-term nitrate concentrations for a variety of recharge scenarios.