“This is one of nature’s processes for purifying water, not only of the land, but of the ocean, and bodies of water deprived of it, other processes are apt to set in. It is, therefore, desirable that nothing should be done to obstruct this beneficial action. We have been informed that the cutting of ice, which was formerly allowed on the Fairmount pool, has been prohibited or discontinued. We would especially recommend that the cutting of ice on the pool be resumed, as an important sanitary measure, on account of the aeration it will afford. If this were done systematically, it might remedy, at least to some extent, the disagreeable odor which we learn is sometimes noticed during the winter.” The aeration adopted by Mr. Moore, Supt. of Cincinnati Water Works, at Eden reservoir, improved the purity of the water twenty per cent., as shown by the analysis of Prof. Stuntz, who recommends the adoption of the process on a larger scale. _Covered Reservoirs_, although used by the ancients, are now being recommended as highly beneficial to the purity of the water, by depriving the organic germs of their propagation elements of light and heat of the sun, preventing freezing of water, and reducing evaporation to a minimum. Paris has two such structures. Chelsea (London) Water-Works has one of ten million capacity that cost $110,000.00. The temporary hardness of water is produced by absorption of carbonates, and may be reduced to softness by: Distillation, Carbonate of soda, Boiling, Caustic lime. Permanent hardness is produced by sulphates, chlorides and nitrates of lime, and magnesia, and can not be dissipated by boiling. An imperial gallon of pure water can take up but about two grains of carbonate of lime, but the presence of carbonic acid in the water will enable the same 70,000 grains (an imperial gallon) to take up twelve, sixteen, twenty, or more grains of the carbonate, and for each grain so taken up is one degree of hardness by the Clarke scale. The system patented by Dr. Clarke, of England, in 1856, is the most practical method for the precipitation of lime, effected by means of a dilution of water with slaked lime, in the proportion of one of lime-water to ten of hard water. The system is in use in several small places in England, notably Canterbury, where 100,000 gallons are reduced, daily, at a cost of twenty-seven shillings per million gallons, with the following results: TOTAL SOLID IMPURITIES. ORGANIC CARBON. ORGANIC NITROGEN. HARDNESS. Before, 33.60 .012 .012 26.3 After, 11.94 .0 .0 4.9 Plumstead water-works, previous to its purchase by the Kent Water Company, of London, reduced, daily, 1,000,000 gallons by the Clarke method. The new owners, however, abandoned it.