UK Water services companies have a statutory duty to supply water compliant with drinking water quality regulations. Twenty percent of Yorkshire Water's supply is from groundwater. Deteriorating groundwater quality has resulted in closure, blending or treatment of sources. Diffuse pollutants of prime concern are Cryptosporidium, nitrate and pesticides. Risk assessments for Cryptosporidium lead to closure of spring sources and installation of membrane treatment for groundwater abstracted from a major chalk aquifer. Upward nitrate trends are observed in many aquifers; the concentration of abstracted nitrate is influenced by water-table level and pumping regimes. Government sponsored schemes to control fertilizer applications have reduced nitrate leaching from soil but not yet affected concentrations in deep well abstractions. Potential pesticide contamination from upland bracken removal has been managed by co-operative agreements with land agents. A major sandstone aquifer has been contaminated by amenity and agricultural pesticides. The implications for the water company of diffuse pollution of groundwater are long term resource reduction, less operational flexibility and increased costs. Groundwater monitoring, trend analysis and UK and international experience of cooperative agreements is discussed with reference to the requirement of the Water Framework Directive and associated Groundwater Directive for measures to protect the water environment.

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