Scheme of Water Supply . 
3° 8 
rjuly. 
Qualities of the Waters from the Permeable Strata. 
In endeavouring to ascertain the qualities of the under- 
ground waters derived from different formations, it may be 
generally assumed that those drawn from limestone forma- 
tions are “ hard ” and those from sandstone “ soft.” Owing, 
however, to variations in the nature of some of the strata 
in different localities, and to the greater or less proportion 
of carbonate of lime, carbonate of magnesia, or oxides of 
iron, &c., which they contain, the quality of the water from 
the same formation is liable to variation according to locality. 
This subject has already been so fully dealt with by various 
authors that I do not consider it necessary to do more than 
give a brief summary of the results as far as they have been 
ascertained in several localities. 
Water from the Chalk. 
From analyses of many wells and springs in this forma- 
tion in the South-East of England, it is well known that 
£C Chalk water ” is hard, though clear and well-suited for 
many purposes, especially in the important one of brewing. 
The percolation of the rain through this formation, 
amounting to about one-third of the adtual rainfall, is so 
exceedingly slow that the water has abundant time to take 
up a large proportion of carbonate of lime from the rock 
itself. The mode of percolation has been ably treated by 
Prof. Prestwich,* Mr. Clutterbuck,t Mr. Homersham, C.E.,I 
and others. It seems, from observations made on the Chalk 
hills by Mr. Beardmore,|| that it takes from four to six 
months for the rain to reach a depth of 200 to 300 feet, so 
that the water which is drawn from this depth in summer 
belongs to the rainfall of the preceding winter. The total 
quantity of solid matter in chalk water varies from 31 to 
32J- in 100,000 parts, of which from 16*4 to 21 parts consist 
of "carbonate of lime. In the case of large works this 
mineral ingredient can be dealt with by the softening process 
invented by Dr. Clark, but for country villages there seems 
to be no plan of easy application for lessening the amount 
of calcareous matter except that of boiling, by which the 
hardness reduced from 247 to 37 in extreme cases. 
* AnnAq^a-ry Address, 1872, p. 41. 
f Proc. Ip$f. Qiv. Engineers, 1842-3 and 1850. 
+ Report, ipommission on Water-Supply, 1S69. 
i) Ibid., fi 204° 
