The great tank at Calcutta, which occupies a space of about ten acres, is not less than two hundred yards from the river. The soil is generally a rich sandy loam near the surface, but becomes rather looser, and inclinable to a fine gravel, after digging about ten feet. The tank may be sixty feet from the top of its banks, (which are level with the streets,) to its bottom; and the river is from four to seven fathoms deep opposite its site. We should conclude that such a distance would secure the waters of the tank from becoming brackish; but the soil favors the communication with the river, and, during the hot season, occasions the tank to be so strongly impregnated as to be unfit for either culinary purposes, or for washing. What is more remarkable, the wells in the different out-works of Fort-William, some of which are four or five hundred yards from the river, partake equally of the moisture: so much, indeed, as to have caused Government to be at a great expence in forming an immense reservoir, (to be filled, if required, by rain water,) occupying the whole of one of the bastions.
It should be here noticed, that, during the rainy season, the rivers are full up to their banks, and run with such force, often six or eight miles in the hour, as to occasion the tide to be little felt, either at Calcutta, or at Dacca; consequently, the whole of the water, both of the rivers, and of the tanks and wells, becomes fresh and pure. On the other hand, during the hot months, viz. March, April, May, and part of June, when, except during a north-wester, or squall incident to the season, not a drop of rain is to be expected, the waters are every where proportionably low; and, as the tides come up with extreme force, we must conclude the portion of sea-water to be very considerable. Such is the fact; for those who visit either Calcutta, or Dacca, at that season, and who drink even of the tank-water, are sure to feel its cathartic effects, and, eventually, to suffer under a very troublesome kind of itch. At Dacca, where the air is more saline, all visitors undergo the penance of a copious eruption: some of the old residents have a return of it every hot season; although they may be extremely careful never to touch river water, but, like the inhabitants of Calcutta, allot a spacious _godown_ to the reception of immense jars of earthen ware, which, being placed side by side, in close rows, are successively filled by the _aub-dar_, or servant whose business is confined to the care, and to the cooling, of water for table expenditure. The water thus preserved is caught in large vessels, placed under the several spouts that conduct it thereto, during heavy falls of rain; the quantity varies according to the consumption, but we may ordinarily compute that of a family at Calcutta to amount to full sixty or seventy hogsheads within the year. In the course of a few weeks, each vessel will be found to contain innumerable larvæ, occasioned by musquitoes, and other insects, and which would, in a certain time, taint the fluid. It is therefore customary to strain the whole so soon as the larvæ are discovered, and afterwards to plunge into each jar an immense mass of iron, made red-hot; whereby whatever animalculæ may have escaped through the strainer may be destroyed. This being done, some alum is dissolved in water, and a sufficient quantity put into each vessel to fine its contents. Some, and I think the practice should be more generally adopted, after the foregoing operations, sprinkle a quantity of very fine sand on the surface of the water in each jar; thereby giving, to whatever gross particles it may contain, a tendency to precipitation. It may, at first view, appear that, in the common course of society, gentlemen must be subject to partake of water which may not have been so scrupulously purified, and perhaps brought from some neighbouring tank, or from a river, impregnated by the influx of a brackish tide. Such may, assuredly, be the case occasionally; but it will be found, on reference to what has been said of the duties of the _aub-dar_, or water-servant, that purified water is carried by a bearer, in a _bangy_, or perhaps in a _soorye_, or earthen jug, to the house at which his master is to dine. In camp, it is a very general custom for every guest’s servant to supply his master with water of his own purifying; which is effected either by means of alum, or of some other astringent producing a similar effect.