158 
J. HOPKINSOX—WATER AND WATER-SUPPLY 
The accompanying map of the Thames Basin (Plate IV) will 
show that our county is already unduly drawn upon by nearly half 
the water-supply for London being derived from the valley of the 
Lea. 
In conclusion, I will just refer to two points connected with the 
future supply of water to London—the possible pollution of the 
Chalk, and the advisability of obtaining a supply of water from 
a distant source. 
On the first point Mr. Baldwin Latham said, in 1884, that “he 
thought it was hardly advisable to go to any great expense in 
taking water from the Chalk, seeing that there was a danger of its 
being seriously contaminated . . .; if the level of the water under 
London were lowered to any great extent, it was quite possible to 
cause a flow back from the lower part of the river (the Thames) 
. . . and eventually the whole body of the Chalk water might 
become contaminated.”*' The more we prevent the pollution of 
our rivers, the more do we pollute the water which percolates into 
the Chalk, for the sewage we divert from our rivers we put upon 
the land, and although much of it is doubtless absorbed by vegeta¬ 
tion and converted into the nutritious products of our sewage-farms, 
much must sink through the superficial soil into the Chalk, and 
this, as the plane of saturation is lowered, will increase in quantity. 
Cemeteries on the Chalk are doubtless very potent factors in this 
contamination ; and cess-pools in it, as they must in time make 
artificial swallow-holes and cause a rapid dissolution of the chalk, 
will add their quota. These, certainly, are decreasing in number 
as systems of drainage are becoming more general; but, with an 
increasing population, the pollution caused by sewage-farms and 
cemeteries must increase to a greater extent than that due to cess¬ 
pools decreases. Percolation through compact chalk will un¬ 
doubtedly render harmless the greater part of any organic matter 
water may contain, but water gets through our IJpper Chalk 
with very varying degrees of freedom, sometimes so freely that 
there can be no possibility of any chemical reaction or mechanical 
filtration. And even when there is such filtration, the well-known 
case of the epidemic of typhoid fever at Lausen in Switzerland, in 
1872, proves that it does not effectually prevent the passage of 
germs of disease. An outbreak of typhoid fever occurred in the 
Furlenthal valley and contaminated the Purlenbach stream, water 
from which percolated through limestone under the Stockhalder 
mountain and rose in a spring at Lausen, forming part of its water- 
supply. The epidemic at Lausen was confined to those who drank 
this water, and experiments were afterwards made which proved 
that the water really percolated through porous strata from the 
Purlenbach to the Lausen spring, not being wholly conveyed by 
channels in the limestone.f 
* ‘ Water Supply and Distribution,’ p. 36. (International Health Exhibition. 
Conferences.) 
f See ‘British Medical Journal,’ 13th March, 1880; also Balfour Browne’s 
‘Water Supply,’ pp. 79-82. 
