A campaigning group believes that former gravel pit reservoirs could provide a viable alternative to controversial plans by Thames Water to raid the River Thames for supplies.

Thames water is proposing to take up to 75m litres of water a day from the river 300m upstream of Teddington Lock and replace it with treated effluent piped from the Mogden sewage works.

However, as revealed by Nub News, the Environment Agency, has suggested this may not be viable or acceptable for the environment.

The scheme could change the chemical make-up of the river water and the temperature, which could harm river life, including insects, plants, fish and birds.

The existing outlets on this reservoir, which supplies water to homes and businesses, are at a level which means they are so high that they cannot access much of the water it holds. Credit: Google Maps.

A consultation on the scheme ended last week and the EA has told Thames Water that it needs to look at alternatives to what is known as the Teddington Direct River Abstraction scheme.

A group of experts and concerned residents from a group called SW Action believe they have identified a better source of water to allow Thames Water can maintain supplies and ensure the taps do not run dry.

Specifically, this would involve using the Queen Mary reservoir, which is close to the line of the M3 near Shepperton. It was the largest reservoir in the world when it was opened by King George V in June 1925.

The existing outlets on this reservoir, which supplies water to homes and businesses, are at a level which means they are so high that they cannot access much of the water it holds.

The group argues that connecting these gravel pits to the Thames would provide extra water in times of drought. Credit: Google Streetview.

A report from SW Action states: "The lower Thames valley has a significant number of large embanked pump storage reservoirs, including the Queen Mary reservoir which was commissioned in 1925.

"Over the decades, the depth of the 285 hectare Queen Mary reservoir has been substantially increased (from 11.5m to approx. 15 m) due to years of extraction of sand and gravel (aggregate).

"As a consequence, the Queen Mary reservoir now has significant 'dead storage' within its structure. This additional storage cannot be readily accessed under normal operating conditions due to the volume of water below the level of the lowest outlet structure.

"Significant modifications to the inlet and outlet structures of the reservoir would be required to enable access to this 'dead storage'. However, if these modifications were made, it would increase the total volume of the reservoir by approximately 10 million litres.

"This additional stored water would be available for supply to the receiving treatment works 365 days of the year, irrespective of any high demand periods."

The report argues other water sources are also available from a cluster of flooded gravel pits in the area.

It states: "The lower Thames Valley has been extensively used for the extraction of sand and gravel, including the freshwater river section traversing the Surrey-Middlesex area.

"Clusters of redundant gravel pits could be directly connected to the Thames river through water channels with sluice gate mechanisms to control water inflow/outflows."

The group argues that connecting these gravel pits to the Thames would provide extra water in times of drought. Importantly, they could also help to combat flooding at other times by taking water out of the river.

In conclusion, the group argues the Teddington scheme, 'does not provide the fastest, cheapest, safest, most effective or reliable option to increase the amount of water required to address future water deficits'.

They add: "In the short-term, an alternative cheaper, faster, more environmentally friendly supply-side solution would be the better utilisation of existing water-related infrastructure (e.g. upgraded inlet and outlet structures to access dead storage at the Queen Mary Reservoir) and adaptation of associated riverine assets to enable incremental enhancement of on-stream / off-stream water storage capacity within the lower Thames reaches."

The report supports the building a massive new reservoir near Abingdon in Oxfordshire, as a medium term solution to providing additional water in future decades.

It also backs the need to do much more to tackle water waste and leaks from the pipes. Currently, Thames Water loses a quarter of all the tap water it treats – 635m litres every day.