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straining surface. This is supposed to prevent the passage of 
even the smallest germs. 
The filtering medium removes iron, lead, sewage, ammonia and 
sulphuretted hydrogen, and reduces the hardness to some extent. 
In conclusion, I think we may fairly assume that we have 
arrived at the following results :— 
That the water supply of large towns is generally in an 
unsatisfactory state. 
That only the mechanical impurities of the water are sought 
to be removed by filtration. 
That this filtering is insufficient for the purpose intended, 
owing to the fouling of the filtering media, and the difficulty and 
expense of cleansing. 
That when chemical impurities exist, and amongst these I 
include excessive hardness of water, no efforts are made to 
remedy the evil. 
That chemical analysis is unable to pronounce absolutely upon 
the wholesomeness of the water supplied. 
And, lastly, that in all cases it should be held as a primary 
condition that the water supplied for domestic purposes should 
not exceed a specified standard of hardness, and that all water 
for drinking purposes should be properly filtered before use. 
