FROM THE CHALK OF HERTFORDSHIRE. 
151 
from the year 1855 no Company was to take water from the tidal 
portion of the Thames, that all river water was to be efficiently 
filtered, and that there were to be no uncovered reservoirs for 
domestic supply within five miles of St. Paul’s, unless the water 
were efficiently filtered after leaving the reservoir. The Thames 
Companies removed their intakes to above Teddington Lock within 
the specified time, and they have taken even more efficient measures 
to ensure a pure supply of water to the Metropolis than they are 
compelled to do by this and other Acts of Parliament.^ 
About 165 million gallons of water are now supplied to London 
daily, 50 per cent, being supplied by the five Thames Companies, 
6 per cent, by the Kent Company, and 44 per cent, by the New 
River and East London Companies. Of the 72£ million gallons 
thus taken from the Valley of the Lea by these two companies,! 
about 60 million gallons are taken from the river itself, and the 
rest from springs and wells, in what relative proportion we do not 
know, but probably at least 10 million gallons are pumped daily 
from the Chalk. These companies, moreover, are frequently making 
new wells and headings, and adding to their engine-power, so that 
the draught upon our underground supply is constantly increasing. 
They have now about twenty deep wells in the valley of the Lea. 
To the amount they abstract, also, must be added that required by 
our own resident population, and if we add the 12 million gallons 
daily taken from the Chalk by the Kent Company, and the amount 
pumped in London by brewers, etc., the drain upon the water in 
the Chalk must be very great. 
It has long been known that, owing to the large amount of water 
abstracted by pumping, the water-level under London is gradually 
sinking, the rate of depression varying from one foot to two feet 
per annum. 
In the year 1821 or 1822 the water-level in a well in the east of 
London stood at exactly Trinity high-water mark, or 12^ feet above 
our present Ordnance Datum. In 1851 its average height was 
43 feet below Ordnance Datum, and in 1881 it was about 105 feet 
below, having thus been lowered 117 feet in sixty years, or at the 
rate of 2 feet per annum. It is now therefore most probably at 
least 20 feet lower, for the abstraction of water goes on at an 
increasing rate. A depression in the plane of saturation at the 
rate of 200 feet in a century must have serious consequences. In 
the centre of London, however, the depression is not so great, for 
the water in the well at the Bank of England has, since the year 
1856, suffered a depression averaging only about a foot per annum. 
There is ample evidence of the extension of this lowering of the 
water-level into Hertfordshire. In fact the depression must have 
been going on from geologic times to the present day, but it is 
* A history of the London Water Companies, and the acts relating to them, 
will he found in Bolton’s ‘ London Water Supply,’ Ed. 2 (1888). 
t The quantity taken by the New Liver Company from the Hampstead and 
Ilighgate ponds for watering streets and flushing sewers, about 1000 gallons 
daily, is so small that it does not affect these figures. 
