The Lincolnshire Chalk aquifer on the east coast of England is used regionally for water supply. However, groundwater abstraction can exceed recharge during times of drought, resulting in saline intrusion. Following hydrogeological investigations in the 1970s and 1980s, a regional groundwater model was developed to underpin the tactical management of the aquifer. Although it is a coarse, single-layer, constant-density model, routine regulatory use of the model since 1988 has enabled a sustainable level of groundwater abstraction to be reached and brought saline intrusion under control. Abstraction rates have been proactively adjusted to suit prevailing conditions using model forecasts. Forecasts are evaluated against model-based thresholds, set by comparing model output (e.g. aquifer–estuary flux) with observed data (e.g. groundwater salinity). The success of the model in managing groundwater resources is attributed to: field-based hydrogeological investigations informing the model design; collaboration between regulators and abstractors, which has built confidence in the model results; commitment to updating the model; and flexibility in the supply network through conjunctive use of ground and surface water. The model has also been applied for purposes not considered during development and has therefore provided value for money for the UK water industry over a 30 year period.