Thames Water has proposed to draw off tens of millions of litres of water a day from the Thames and replace it with treated effluent from the large Mogden sewage works in west London to help tackle water shortages.
The company, which leaks 630m litres a day from its network, is putting forward what it calls a “water recycling” plan to cope with shortages resulting from the rising population and predicted droughts caused by climate change over the coming decades.
It first suggested the plan in 2019, but it was rejected by the Environment Agency because of the anticipated unacceptable impact on the environment of releasing millions of litres of treated effluent into the river. The effect would be to raise the temperature and salinity of the water and have an adverse impact on its ecology, particularly affecting migratory and indigenous fish.
But the water company has put forward the Mogden proposals as the cheapest and quickest option in its new draft water resources management plan to tackle predicted serious water shortages over coming years. It wants to abstract up to 150m litres of water a day from the Thames above Teddington lock in south-west London, and transfer it by a pipeline to reservoirs in the Lee Valley in east London.
The abstracted river water will be replaced by treated effluent from Mogden, one of the biggest sewage plants in the UK. But technical documents within Thames Water’s resources management plan show there were still environmental concerns with the water reuse proposal.
Associated documents say the proposals will have potential to cause increased water temperatures and a change in the salinity of the river. There could be impacts on freshwater and estuarine fish, their migration patterns and the life-cycle of macroinvertebrates – insects in their nymph and larval stages, which are a key indicator of river health.
The proposals could also harm other key parts of the river ecosystem and could breach regulations on the chemical status of the river, which measure the levels of pollution in a waterway. The draft plan is being put out to consultation via public meetings, which start on Monday.
English rivers are already suffering from the impact of chemical and biological pollution from treated effluent released by water companies, and runoff from agriculture and roads. No English river is considered to be in a good biological or chemical state.
Thames Water said in its proposals the idea was the most cost effective and quickest to deliver to build in future resilience for the benefit of customers, their children, grandchildren and the environment.
“We need to improve the resilience of our water supply by the early 2030s,” the company said. “This scheme will help keep the River Thames flowing and can be introduced within eight years, helping us achieve resilience to a one-in-200-year drought event by 2031.
“There are other schemes that we could deliver within eight years … but these are all more expensive.”
The company said £13bn will be invested between 2025 and 2050 in protecting water resources. Customers will pay for this via their bills, which are likely to rise by about £100 by 2050. It forecasts an extra 1bn litres of water will be needed each day by 2075 to accommodate global heating and population growth.
“The majority of the investment is to ensure we can cope with our changing climate and can continue to provide a secure water supply, as well as protecting and improving the environment for the long-term,” Thames said.
The sewage reuse plan would involve creating a new abstraction site on the Thames between Teddington weir and Hampton Court Palace to abstract up to 150m litres of water a day, transferring it across London to the Lee Valley reservoirs in the east of the city, and replacing the flow with highly treated water from Mogden via a new 15km (10-mile) pipeline.
The water will be provided not just for Thames customers but other water companies in the south-east, including Affinity Water.
Thames Water says the reuse proposal would require regular maintenance of the treatment plant. Mogden, the third largest sewage treatment plant in the UK, has been criticised in the past for leaking raw sewage into the Thames. A report by the House of Commons’ environmental audit committee said that 2bn litres of untreated sewage were discharged into the Thames in two days in October 2020; the equivalent to 800 Olympic-sized swimming pools of diluted raw sewage.
Thames Water has other plans to tackle future water shortages, including by reducing its own leakage, estimated to be 630m litres a day, encouraging the public to reduce their water use, installing more smart meters and building a giant new reservoir south of Abingdon in Oxfordshire.
Feargal Sharkey, former lead singer of the Undertones and a water quality campaigner, said: “It shows how utterly desperate these companies have become that they are contemplating this kind of insanity and the Environment Agency should put a stop to this immediately.”
Thames Water said: “The Environment Agency has been involved in the development of the proposals included in the WRMP [water resources management plan] to date. A full environment impact assessment is being undertaken and will be submitted alongside the planning application that is required to be able to build the scheme.”
The company added that the south-east faced substantial water shortages, and the extreme heat and lack of water last summer was a clear indication of the climate emergency first-hand.
“The scale of the water resources we need for the future means we need to take a strategic approach to planning our future water supply,” the company said. “We’ve been working closely with other water companies to look at options that could provide a large volume of water – more than 50m litres of water a day – for more than one water company to use.”
