Thames Water Ring Main, Water pipe and tunnel in England, United Kingdom

Thames Water Ring Main is a large water pipe and tunnel network that circles beneath London. It consists of a deep underground ring that carries treated water from treatment works to storage reservoirs across the city.

The ring main was built in stages between the 1980s and 1990s to improve water distribution and reduce reliance on older mains. It was later extended to connect more treatment works and reservoirs.

The ring main is a key part of London's water supply system, though it remains hidden from view. Its presence is occasionally marked by small surface structures like shafts and valve houses that blend into the urban landscape.

The ring main is not open to the public, so you cannot visit it directly. However, you can see related infrastructure such as pumping stations and reservoirs from the surface, and some parts are visible during open days or guided tours.

The ring main is one of the largest water supply tunnels in the world, yet most people walk above it without knowing. Its depth and length allow it to store and move large volumes of water efficiently across the city.