Ever wondered where a third of London’s water comes from? It’s treated right here at Ashford Common Advanced Water Treatment Works. This crucial facility ensures millions have access to clean water every day.
Ashford Common water treatment works is located in Ashford Surrey. It plays a vital role in supplying potable water to west London. The plant connects to the local distribution network and the Thames Water ring main.
Originally constructed in the 1950s, Ashford Common underwent significant modernization in the 1990s. This upgrade increased its output to meet the growing demand for water in London.
After World War II, London anticipated a surge in water demand. In 1947, the Metropolitan Water Board proposed building a new water treatment works. Ashford Common was chosen for its location between Ashford and Sunbury-on-Thames. The works would draw water from the nearby Queen Mary Reservoir. It would also use the Staines Reservoir Aqueduct.
Water travels through the Ashford Common tunnel. This tunnel stretches 1,882.6 feet. That is 573.8 metres long. It measures 8 foot 4 inches in diameter. That’s 2.53 metres. The tunnel lies 46-48 feet below the surface. This is 14.02-14.63 metres. It runs through London clay. The West shaft connects the tunnel to the reservoir. The East shaft supplies water to the treatment works inlet. Designed to carry 200 million gallons per day. That is 909,218 cubic metres. Tunneling began in January 1952. It finished in May 1952. The tunnel first filled in March 1953.
Early treatment processes included aeration. Fine screen filtration removed algae. Slow sand filtration and granular carbon treatment followed. Sterilization and contact tanks completed the process. Rotating screens proved most effective for primary algae filtration.
By 1953, Ashford Common works was under construction. It featured 24 micro-strainers. It also had 32 slow sand filter beds. Each bed covered about three-quarters of an acre. This is 3345 square metres. Filters were cleaned every 25 to 30 days. Workers skimmed off the top inch or two of sand. This sand was cleaned and returned. The plant also included aeration basins. It had a chemical treatment plan. There were two contact and balancing tanks. High and low lifting pumps were installed. Designed as two parallel plants. One side could close for maintenance. The other side would maintain the majority of the demand.
Fully commissioned in 1958, the works initially treated 108 million US gallons per day. This is 409 megalitres. Peak output reached 480 Ml/d. Higher flows were possible up to 550 Ml/d. However, this increased filter cleaning frequency.
For four decades, Ashford Common operated effectively. In the early 1990s, increased water demand prompted upgrades. These upgrades increased the hydraulic capacity.
Modern facilities at Ashford Common included stored water pumps. These pumps drew from Queen Mary and Wraysbury reservoirs. Pre-ozonisation provided five minutes of contact. Rapid gravity primary filters used dual media. Air scour and water backwash cleaned the filters. Main ozonisation offered 16 minutes of contact. Slow sand filters contained granular activated carbon. Low lift pumps and hypochlorite dosing were used. Contact tank screens measured 400 μm mesh. Chlorine contact tanks were installed. Hypochlorite, sodium bisulfite and ammonia dosing occurred. High lift pumps distributed water.
Subsidiary plant included ozone generation. A washwater treatment plant was added. SCADA monitored and controlled water flow. With these upgrades, peak supply rose from 480 Ml/d to 690 Ml/d.
Ashford Common continues to evolve. In recent years, motor upgrades have enhanced reliability. Bespoke engineering solutions have addressed unique challenges. These improvements ensure the plant can continue to deliver clean water. WEG and Thames Water partnered to replace large pump motors. This critical upgrade ensures a reliable water supply for London.
So, as you turn on your tap today, remember the complex processes. Remember the history and the continuous improvements made here at Ashford Common Advanced Water Treatment Works. It’s a vital part of London’s infrastructure.