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Claremont Square Reservoir
Claremont Square, Islington, London, UK
associated engineer
William Chadwell Mylne
date  1855 - 1856
era  Victorian  |  category  Dam/Reservoir  |  reference  TQ310831
This service reservoir in the centre of Claremont Square was built to boost water supplies from the New River. The 17th century New River brought fresh water to London from springs in Hertfordshire, but within a century demand was outstripping supply. The present covered reservoir replaces an 18th century open-air one, and is still in use.
New River ó no longer new and more of a canal than a river ó was built in 1608-13 by Sir Hugh Myddelton (1560-1631). By the beginning of the 18th century Londonís burgeoning development meant that water supplies could be inadequate. To create a buffer against varying flows and to give extra head of water to the gravity supply, the New River Company constructed an Upper Pond that would supply the riverís terminus at Round Pond (TQ313827). It was built on 0.4ha of land leased from the second Earl of Clarendon, Henry Hyde (1638-1709), and was completed in 1709.
Apart from continuing supply problems, a cholera epidemic in 1846 prompted safety concerns and led to the Metropolis Water Act of 1852. This stipulated that all water, other than from pumped wells, should be filtered and that all filtered water reservoirs within an 8km radius of St Paulís Cathedral should be covered.
The Upper Pond was demolished in 1855 and replaced by a brick structure 38.6m above high water in the River Thames, which also delivers water by gravity flow. Some of the original timber supply pipes were found during excavations for the new service reservoir.
The reservoir is about 55m square with rounded corners. Inside it is divided into 12 north-south bays separated by partition walls, which support the barrel-vaulted roof. Each partition wall has 10 narrow openings under segmental arches along its length to allow water to circulate. There are also two east-west cross walls with arched openings into each bay. The brick floors in each bay are slightly concave. The structure is about 8m deep and contains water up to 6.4m deep, with has a capacity of 16 million litres.
The 610mm diameter cast iron inlet pipe is on the south side, and is opened by a gate valve with a control rod that rises through the roof. There are similar arrangements for the three outlets (south west, north east and north west corners). All four control mechanisms are set on shallow plinths of York stone. There is a 2m wide channel along the south side, sloping to a drain at the west wall, which also has York stone floor slabs. Two additional outlets were set into the west wall at a later date.
All the bricks in the structure ó reputedly 4 million of them ó are mortared together with hydraulic lime. The outer wall is battered at a slight angle, and is kept watertight by an external layer of puddled clay. However, little of the reservoir is visible externally as it is concealed within a grass-covered earth embankment some 4m above ground level. A low brick parapet wall with stone capping rises above the mound and surrounds the grassed roof, which has eight round equipment hatches with metal covers.
Access to the interior is through a stone roofed entrance on the east side, leading down two flights of stone stairs with iron handrails. It is not open to the public. The embankment is still ringed with the original iron railings at street level. The structure cost £21,000 to build ó a price that reflects the fact that water supplies to customers had to be maintained throughout construction.
The reservoir is now owned and operated by Thames Water, and is supplied with treated water from the Thames Water Ring Main (completed in 1994 and extended in 2010). It was Grade II listed in June 2000.
William Chadwell Mylne was the second son of Robert Mylne, surveyor for the New River and designer of the first Blackfriars Bridge (River Thames, now demolished). William succeeded his father as surveyor to the New River Company in 1811.
Clerk of works: Mr Scott
Research: ECPK
The Illustrated London News, London, 22nd November 1856
"Covered Service-Reservoirs" by William Morris, in ICE Proceedings, Vol.73, pp.1-33, London, January 1883
reference sources   CEH Lond

Claremont Square Reservoir