Name of Company. Maximum. Minimum. Average. Kent 1.0 1.0 1.0 West Middlesex 4.3 2.0 3.0 Grand Junction 4.9 2.4 3.3 Chelsea 7.1 2.3 3.7 Professor Frankland remarks that the water of the Thames is at its source as free from pollution as the chalk well water, but on its downward course becomes largely and progressively contaminated by sewage and the washings of cultivated land, especially during winter. The average hardness of the Thames water—or the weight of carbonate of lime, or its equivalent of other soap-destroying substances, found in 100,000 parts of water was 21° or parts in 1873, and 19.7° in 1874. Large quantities of soap or soda are required to soften the water before it is used for washing; but this process could be accomplished for a small portion of the expense by substituting lime for soap or soda, as practised on similar waters at Aylesbury, Canterbury, Caterham, and Tring. The following table exhibits the degree of efficiency of filtration of the waters:— Name of Company. No. of occasions No. of occasions No. of occasions No. of occasions when clear and when slightly when turbid. when very transparent. turbid. turbid. Chelsea 6 5 0 2 West Middlesex 12 1 0 0 Grand Junction 7 5 1 0 The exceptional occasion on which the water supplied by the West Middlesex Company was slightly turbid was in December, when the condition of the Thames was bad for a lengthened time, so that even the large storage of the Company proved insufficient to render them independent of flood water; it being impossible, moreover, to separate by filtration the whole of the finely divided clay to which the turbidity of the water was due. The Kent Company’s deep well water, having already undergone natural filtration through an enormous thickness of chalk, is always clear and transparent, without artificial filtration. The appliances of the Companies supplying river water are, excepting in the case of the West Middlesex Company, unequal to the filtration work required of them. The microscope is called into use in the examination of potable water, and it always reveals numbers of living and moving organisms in the sediment deposited by turbid water on standing. The annexed table exhibits the results of such microscopic examinations during the past six years:—