Under northeast London lies Britain’s only artificially-recharged aquifer used for public water supply.
North London Artificial Recharge Scheme (NLARS) uses a chalk aquifer beneath Enfield, Haringey and the Lee Valley which we top up with treated water when rainfall is plentiful to use as a back-up resource to boost supplies during droughts.
How it works
The chalk rock acts like a big sponge, holding water for when we really need it. It is what’s known as a ‘confined aquifer.’ It is confined by a surface layer of less permeable London clay, which protects the groundwater in the chalk beneath. This makes it less leaky so the water that occurs naturally in it, together with the water we add in artificially, does not disperse.
These aquifers were first artificially recharged back in the 1890s by what was then the East London Water Works Company. Further larger-scale trials were carried out by the Metropolitan Water Board in the 1950s, before work on the project in the 1970s by what was then the Thames Water Authority. This later became a private company, Thames Water Utilities Limited, in 1989.
We have used the NLARS since 1995. After the 2006 drought we spent £6m to improve its potential daily output from 150 million litres a day (enough for 1m people) to 180 million litres a day per year.
The scheme is designed to be able to provide additional water during extended droughts, with its daily output starting off at around 200 million litres, decreasing to around 140 million litres as the water stored in the aquifer is used up.
Facts about NLARS
- NLARS can supply 180 million litres a day of extra water – enough for 1.2m Londoners – when needed.
- 48 boreholes can take water out of NLARS when needed. We use 31 of them to artificially recharge NLARS when there is water to spare, at a rate of between 35 to 40 million litres a day.
- Six new boreholes were built in 2006, helping boost its maximum average daily output by 20%.
- Water drawn from NLARS is pumped into the New River before being treated at either Hornsey, Chingford or Walthamstow water treatment works.
- NLARS has been used during dry spells in 1997, 2003, 2005, 2006, 2018 and 2019.
Additional back-up water source
Our Thames Gateway desalination plant, which treats water from the tidal River Thames, was opened in 2010 to provide greater resilience during long periods of low rainfall. The facility is capable of putting an additional 150 million litres a day into supply, which is enough to supply one million people.