SYNOPSISAnImprovedmethod has been developed to assess and control the quantity of water available to river abstractors. The methodology quantifies the sensitivity of the river environment to abstraction by a weighting system, and uses this to establish, on a subcatchment basis, maximum permissible volumes of abstraction and minimum permissible river flows. Guidelines developed from the methodology have been used as the basis for determining applications for abstraction licences in North Yorkshire, before being extended to cover the rest of the Yorkshire Water area.