About 70 per cent of the water we supply comes from underground sources (groundwater); predominately chalk but also greensand.

The remainder comes from rivers and storage reservoirs. The majority of water we supply is hard as it comes from the chalk but the hardness varies from source to source.

Water stored in these sources has filtered through numerous rock layers underground and is drawn to the surface through man-made boreholes which can be up to 250 metres deep.

We operate around 200 of these boreholes across our service area.

The map above (click to enlarge) shows the geology of the British Isles and the extent to which we rely on groundwater in our region.