Water pollution regulation is devolved in the UK. Surface, coastal and ground waters in England suffer from significant pollution problems: 78% of surface and groundwater bodies fail to meet the ‘good’ ecological status prescribed by the EU Water Frameworks Directive. Pollution increases water treatment costs and adversely affects wildlife. Compared to treatment, preventing water pollution at source can have a cost-benefit ratio as high as 1:65. This POSTnote describes the contribution of agriculture to water pollution, and measures that can be taken to reduce it.