From 2 April 2018 new rules for all UK farmers in England will be introduced by the Environment Agency to help protect water quality. The rules require farmers to prevent soil erosion, adopt nutrient management planning, and protect surface waters directly from livestock, fertilisers and manures.
The rules were drawn up in collaboration with farming and environment stakeholders and will be implemented through an advice led approach, working with farmers to meet the requirements before enforcement action is taken.
More info: New Farming Rules for Water - GOV.UK
Guidance here: Rules for farmers and land managers to prevent water pollution