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around through leaky joints, and contaminate the water when it is next turned on, so that it frequently happens that the first water that comes into the cistern when it is turned on is quite unfit to drink. There is an enormous amount of loss with this system, which might, however, in great part be prevented. The last disadvantage of the intermittent supply lies in the fact that some delay is frequently experienced in obtaining water for extinguishing fires.
With the system of constant service, on the other hand, the pipes are always full, and so it is not necessary to have cisterns, or receptacles of any kind for the storage of drinking water, although this is frequently done. Receptacles are, however, necessary for the supply of water to closets. The pipes being always full of water under pressure, are far more likely to leak out into the soil than to be contaminated with foul matters from the soil. Still, it is not advisable on any account that water-pipes should be carried near to sewers or other sources of contamination. The water is fresher, and purer, and cooler in summer when supplied on the constant service system. The pipes are full in case of fire, and the inspection of pipes, taps, and other fittings is, as a matter of fact, carried on very much better, and less waste of water takes place under this system (although the pipes are always charged) than under the other system. It is obvious that, unless there were very strict supervision, a great waste of water would necessarily accompany the use of the constant system. For this reason, also, the water companies that have adopted that system will not allow waste pipes from cisterns to be connected with the sewers, or closet apparatus, but insist on their discharging freely in the open air; and usually in some place where any waste water run. ning out of them would produce annoyance, so that it would be speedily noticed, and the cause of the waste remedied. It is very important, however, where this system is adopted, that there should be double reservoirs or tanks, in
order that one may be used while the other is being cleared out; for if, as has been the case at some places, and notably at Croydon, the water be supplied by the intermittent system of service for a few days, defects which have produced no inconvenient results while the constant system of supply was practised (such as the connections of water-closet hoppers directly with the main water pipes), the possibility of the existence of leaky joints in the mains, through which foul matters may enter from the soil, etc., may produce the gravest results by spreading enteric fever throughout the community; and here I may mention that it is, of course, extremely improper and very dangerous to convert a cistern which is used to supply drinking water, or a water supply pipe, directly with the hopper of a water closet. The system of constant service is coming gradually into more general use, and it is very probable that water meters will be much more generally used than they are at present. A simple apparatus of this kind
is Ahrbecker's water-meter, in which the water is made to pass through oblique apertures in a fixed plate into oblique or spiral passages in a cylinder which is capable of rotating, and the axle of which turns the index of a dial. The pipes, by means of which the supply of water is conveyed into the houses from the mains, are usually made of lead; this material being preferred on account of its durability, and the facility with which it can be bent in various directions. A disadvantage of it is, that certain waters attack and dissolve lead, and are thereby rendered more or less poisonous. Those, however, are chiefly pure and soft waters. Waters containing mineral salts in solution, such as those generally supplied for drinking purposes, scarcely attack lead at all; and, moreover, with waters which do attack lead, the surface of the metal becomes covered with an insoluble coating of oxide and carbonate, which protects it from further attack. Pipes made of lead lined with a thin layer of tin are sometimes used, but when the tin becomes damaged in any way, a galvanic action is set up, and the lead is dissolved quicker than ever. Varnishes of various kinds have been proposed for coating the interior of water mains and pipes. Most of them are very objectionable— one of them positively containing arsenic. Wrought iron pipes with screw joints are sometimes used for water pipes. They are certainly cheaper than lead, and it is said that they will last longer. Bends are made of almost every possible shape just as in gas pipes. In some rare instances lead pipes are attacked from the outside by water containing carbonic acid in the soil, as shown in a sample of a lead pipe which had been laid in chalk, and which was contributed to the Parkes Museum by Mr. Bostel, of Brighton.