It was owned by Veolia Environnement, a French company with international interests in the water, waste management, energy and transportation sectors.

The area served lay to the north and west of London, including parts of Hertfordshire, Bedfordshire, Buckinghamshire, Essex, Middlesex and Surrey.

This may have been a contributing factor in the outbreak of Cryptosporidium parvum in March 1997 when Three Valleys had to ask 300,000 consumers in Hertfordshire and thousands more in the London boroughs of Harrow and Brent to boil water.

The source was never isolated though several water supply boreholes in the Chalk aquifer between St Albans and Bushey contained the pathogen.

After the major fire at the Hertfordshire Oil Storage Terminal at Buncefield in December 2005, efforts were made to deal with contaminants to the local aquifer and bore holes.