Thames Water Ring Main

The Thames Water Ring Main (TWRM) (formerly the London Water Ring Main/LWRM) is a major part of London's water supply infrastructure, approximately 80 km (50 mi) of mostly 2.54 m (100 in) concrete pipelines to transfer potable water from water treatment works (WTWs) in the Thames and River Lee catchments for distribution within London.

The initial ring was constructed by Thames Water between 1988 and 1993. There are plans for further extensions through to 2025.

Moire information on the Wikipedia page