“Portsmouth Water has observed a long-term rise in nitrate levels in groundwater within its supply area. A key contributor to this increase has been due to the high use of – and leaching of – nitrate fertiliser, particularly in past decades, with further contribution from intensive livestock farming. The presence of many karst features prompted the company to also consider the potential risk of FIOs in raw water supplies, derived from both livestock farming and the increasing number of equestrian activities.”