Nitrate concentrations in the major aquifers of the UK continue to rise at about 0.4 mg/l/year, although the problem has been known about for several decades. Pesticides have also widely detected in groundwater. Unsaturated zone thickness and aquifer properties mean that changes in agricultural practice may also take decades before the full beneficial impact is seen. \ud A national study carried out on behalf of UKWIR has shown that about 2450 Ml/d, almost 50% of the groundwater used for public supply, currently is estimated to require action to mitigate quality problems. This reflects a combination of deterioration in groundwater quality and introduction of more stringent regulatory standards for drinking water. Expenditure has been largely for mitigation of nitrate, pesticides, Cryptosporidium, arsenic and hydrocarbons/solvents. Groundwater quality problems in the UK have cost the water industry £754 million between 1975 and 2004 at 2003 prices, mainly for capital investment.\ud Assuming that current practices, water demand, climatic conditions, quality drivers and regulatory setting do not change, future capital investment costs could be at least £73 million and possibly as much as £180 million for each future 5-year AMP period with increasing operating costs as the total volume of water treated rises. By 2027, the volume of water that might have to be treated or replaced may have doubled from the current level and almost all groundwater would need to be treated.\ud The potential impact of possible curtailment of water treatment under the Water Framework Directive was evaluated, using the assumption that no further treatment of groundwater would be permitted after AMP4. Under this scenario, some 1800 Ml/d of water (35% of the total groundwater supplied) would have to be replaced by 2027. Groundwater in most areas of the major UK aquifers is already fully exploited so other sources of water would need to be found. These could range from surface water impoundments to effluent reuse and desalination. All of these would have serious financial and regulatory implications with potential capital costs of the order of £2 billion.\u
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