They are the privileged band of just over 50 exclusive addresses that enjoy their own private water supply, and they range from stores such as Harrods and Simpson's of Piccadilly to clubs including the Army and Navy and the Hurlingham, and a group of financial institutions headed by the Bank of England.
These are properties that have their own boreholes or artesian wells, in some cases very old, sunk through the London clay into the chalk beneath, which is one of Britain's richest aquifers (water-bearing layers of rock, containing many millions of gallons of water).
Underneath the riches on display at Harrods, the chic Knightsbridge store has another treasure - an abundant source of cheap water in its basement. Its needs are met by three boreholes that reach 150 metres below Brompton Road and can deliver up to 1,091 cubic metres of water a day.
This system saves Harrods an estimated pounds 200,000 a year in water bills. "We draw all our water needs from our own supply," said Peter Willis, a spokesman for the store. "Last year we took 230,000 cubic metres.
"The water is constantly monitored and treated to ensure that it is safe for human consumption. We considered bottling it at one stage, but it was deemed not to be economically viable."
If Harrods was contracted to Thames Water for its supply, it would have to pay 93.97p a cubic metre for its water. After licence fees are met, the water from its own wells costs just 0.5p a cubic metre.
The Bank of England is another institution with cause to celebrate: the Old Lady of Threadneedle Street is also sitting on countless liquid assets. Officials at the bank calculate that they save 20 per cent of their total water bill by using their own supply.
"We used the water pumped from our own wells for all purposes until about five years ago, when an EC directive indicated that there were too many minerals in it," said the bank's Carol Elliot. "We now take our drinking water from a separate feed from Thames Water."
However, the bank plans to continue drawing its licensed 36,368 cubic metres of water a year because it believes it is being public-spirited in helping to keep down the water table beneath London, which is rising.
A range of other financial institutions are in the same happy position. They include Lloyds Bank in Lombard Street, the private bank C Hoare and Co, of Fleet Street and, most enterprisingly, the Abbey National, which once successfully bottled its own water. Its supply is at its HQ, which encompasses the fictional home of Sherlock Holmes at 221b Baker Street.
"The boreholes were drilled when the building was constructed in the early 1930s," said Abbey National spokesman Tony Wells. "It was refurbished in 1981 and the then chief executive, Clive Thornton, thought that after the piping and pumps had been replaced, it might be a good idea to market the water from our own wells.
"The water was sold for charity but before long the scheme was abandoned, and ever since bottles of Abbey water have become collector's items."
One of the biggest users of London's secret water supply is the exclusive Dolphin Square flats complex, until recently the home of the Princess Royal. The block of 1,200 apartments facing the river at Chelsea includes a swimming-pool, restaurant and leisure centre.
"The four boreholes supply our needs," said general manager Tony Crawford.
"We treat the water for drinking purposes, and this is measured by environmental health officials, and I'm delighted to report that we have no trouble achieving a clean bill of health. The wells save us money, and mean we are never under threat of running short."
It is estimated that it can cost up to pounds 20,000 to bore and equip a well deep enough to draw off the water accumulating beneath the city. MPs are the most recent group to benefit.
The Parliamentary offices located above Westminster tube station are to have their own supply in the near future. The construction work to tap into the water supply was carried out during the building of the new Jubilee Line extension.Reuse content