Mr Burn advocates the employment of a compound of tar, which, he says, most effectually protects them. Zinc, although cheap, and little acted upon by water, is seldom employed for cisterns. Dr Osborne says he has seen several cases of zinc poisoning, caused by drinking water that had passed through zinc pipes, or had stood in zinc pails. Equal, if not greater risk is incurred when drinking-water is kept in lead cisterns, or is made to run through lead pipes. In setting up cisterns or tanks made of stone or cement, common mortar must not be used, as lime is taken up and the water is rendered hard in consequence.
In seasons of drought it is by no means an unusual occurrence for many rural districts to lack a sufficiency of water, the limited supply of which entails considerable suffering, sometimes terminating fatally upon farm stock, with frequent loss to the owners. Few persons, perhaps, can form a correct idea of the immense quantity of water that in the shape of rain falls even in the least humid portions of our islands. If this rain, which is now allowed to run waste, were properly collected and stored, it would form a valuable resource in times and at places where there was a dearth or scarcity of this necessary element.
Mr Bayley Denton, writing on this subject, says:—“Take an ordinary middle-class house in a village with stabling and outbuildings, the space of ground covered by the roofs will frequently reach 10 poles, while the space covered by a farm-labourer’s cottage and outbuildings will be 21⁄2 poles.
Assuming that the roof is slate and the water dripping from it is properly caught by eave-troughing, and conducted by down-pipes and impervious drain-pipes into a water-tight tank sufficiently capacious to prevent overflow under any circumstances, and that by this method 20 inches of water from rain and dew are collected in the course of the year, the private houses will have the command of 28,280 gallons, and the cottage 7070 gallons in a year.... A tank 16 feet long, and ten feet wide, will hold 1000 gallons in every foot of depth, and where the water is not wanted for drinking, it need not be covered,
except with a common boarded floating roof of half-inch boards fastened together. This floating roof keeps the water clean, and prevents evaporation.”[222]
[222] ‘On the Storage of Water,’ by Bayley Denton.
Leakage of pipes of any kind into a cistern or tank should be particularly guarded against. Another important precaution claiming adoption is to see that the overflow-pipe is not directly connected with the sewer, for if it be, the sewer gases will rise through it, and being prevented escaping from the cistern because of its covering, will become absorbed by the water. To obviate this, the overflow-pipe is curved, so as to force a syphon trap; but this device conduces to a sense of false security, since it mostly fails owing to the evaporation of the water in it, or to the gases forcing their way through it. The overflow-pipe, therefore, should never have direct communication with the sewer, but should always end above ground, and discharge over a trapped grating into it. For similar reasons the same tanks or cisterns should never supply the water used for culinary or drinking purposes and also the water-closets.
To the water in the tanks attached to these latter, some disinfectant substance should from time to time be added; more particularly during hot weather.
Unless a cistern be efficiently protected, particularly if it be placed in an exposed situation, various disgusting and filthy substances, such as the ordure of birds, cats, rats, and dead insects, &c., will be liable to fall into it, and foul its contents. This must not only be guarded against by the proper means, but even where the contamination may not be suspected, or likely to occur, the cistern should be frequently examined and periodically cleansed; part of the proper carrying out of which should consist in always running off the water remaining in it and renewing it with fresh.
The London and General Water Purifying Company have adopted an excellent idea in connection with tanks and cisterns; they fit them with filters, so that the water drawn from the pipes shall have been submitted to filtration previous to delivery.