Groundwater levels

About 70% of the water we supply comes from underground sources (groundwater).

Our main water sources

70% groundwater

As rain soaks through the ground it is stored in 'aquifers'. We pump this water (groundwater) to the surface where it is treated and supplied to you.

23% rivers

We take water from rivers to fill our reservoirs, or to pump directly to water treatment works for supply. More than 15% of the water we take from rivers comes from recycledwater which has been cleaned at our wastewater treatment works and released into the river.

7% reservoirs

We have four reservoirs, the largest is Bewl Water on the Kent/Sussex border, followed by Weir Wood, Darwell and Powdermill in Sussex.

Drought triggers

The drought status in any area is based on several factors including historic rainfall, groundwater and reservoir levels. If a groundwater drought trigger level is met this does not necessarily mean the overall drought status has changed.

Drought trigger curves are based on those in Southern Water’s current Drought Plan published in 2013. Some of these curves are being updated as part of the process to update the Drought Plan, a final version of which is due to be published later in 2018.


Groundwater is measured in Metres Above Ordnance Datum (mAOD). mAOD is based on the mean sea level at Newlyn in Cornwall and is used as the reference point to calculate height above sea level in the UK. 

See the current groundwater levels below:



  Impending drought


  Severe drought








Contains Environment Agency information © Environment Agency and/or database right.

Regional rainfall
Reservoir levels