The average of requirement (estimated from the consumption of large communities) would probably be about 12 gallons per person per diem; making an amount, for the total population of the City, of about 1½ million gallons per diem. Assuming this estimate to be correct, a point which I would beg you to observe is the following: that, although there might be very little fluctuation in the _total quantity consumed_, and although it might remain constant at the figure I have given, yet in the items of individual consumption, making up this gross amount, there would be almost infinite varieties. One family would habitually consume twice as much water as another family of the same size: one family would consume six gallons per person on five days of the week, and would require all its remaining quota on the other two days; and so forth. These differences and caprices of individual requirement do not sensibly affect the total quantity consumed in a given week by a population of 130,000 persons; one consuming more, another less, the first counterbalances the last in forming the materials for a fair personal average; and a source of supply calculated from such an average for a large population would, practically speaking, be unlimited to each individual consumer, provided only that it were so distributed, that each consumer could draw from the common stock at his own time and according to his own necessity. This advantage is obviously lost under the present system of intermittent supply, which compels a larger total distribution than would else be requisite, entails the expensive and unwholesome necessity for storage, and yet is notoriously fraught with the inconveniences of a restricted source, or a defective supply. I have no sufficient data for judging with precision what quantity of water might be required to fulfil all those public purposes of cleanliness and of protection from fire, to which I have adverted. The supply would require to be _practically_ inexhaustible; but the consumption, on an average of the four seasons, would probably lie considerably within half a million of gallons per diem. When the distribution of water is brought into its proper relations with the drainage of the City--that is, when the arrangements of domestic drainage are completed, in conformity with the intentions of the Act of Parliament, and when all the water, distributed for private consumption, is made to traverse and to cleanse all the channels of house-drainage, it is probable that a smaller quantity of water than is now consumed will suffice for the flushing of sewers, and for other so-called sanitary purposes.