of brick laid in Portland cement. The water in the cistern filters slowly through the brick work of the cylindrical chamber.

It is considered that filtration through stone or brick, while slow, is very thorough. The slow rate of filtration is offset by the large area of filtering surface which the brick filtering chamber presents. The cistern should be lined throughout with Portland cement. Fig. 246 gives a very good method of construction for

a cistern overflow. The overflow is made of tile pipe, and as shown, it is laid along the bottom of the cistern and carried up to the level desired for the overflow, and there connected to the outlet. This form of overflow will carry off much of the sediment and filth accumulating in the cistern, thereby rendering it necessary to make less frequent cleanings of the cistern.

The same illustration shows a good method in connection with

the well pipe of a cistern in the use of a return bend on the end of the pipe.

A straight pipe ending close to the bottom of the cistern will suck up sediment, while in the use of the return bend the suction draws the water into the pipe in a downward direction.

In Fig. 247 is shown another combination of cistern and filter which may often be used to advantage, especially in locations where rain water must be depended upon as a drinking supply at certain seasons of the year, or at all times. The illustration

shows a common cistern, into which is built a filter having an arched surface, and constructed of two courses of brick, with a space of 2 or 3 inches between them. This space is filled with charcoal, which is an excellent filtering material.

In connection with the cistern and filter, a well is used, made as deep as practicable, into which the filtered water is discharged from the filtering chamber. The well is made waterproof. This method allows pure drinking water to be pumped, of the same cool temperature as ordinary well water.

CHAPTER XXII

HOT AND COLD WATER SUPPLY

THE work of the plumber is divided into two distinct lines— drainage and supply.

In nearly all city work, the drainage system must be installed according to plumbing ordinances established for the purpose of securing uniformly sanitary work.

The supply system, however, in most cases is not thus protected by municipal ordinances, although in some of the more progressive cities it is now safeguarded in the same manner as the drainage system.

There was a time when nearly all supply piping was of lead. To-day, however, the use of this material has been very largely displaced by the use of brass and galvanized wrought iron. It may be stated, however, that in some sections lead pipe is still used almost entirely for supply work, generally in such cases, owing to the chemical properties of the water supply.

Some waters will attack lead pipe more seriously than wrought iron, while the reverse may be true of other waters.

Thus, in some sections galvanized piping will fill with rust and sediment in a very few years, while over the surface of lead pipe a sort of protective coating will form, which will allow its continued use for an almost unlimited length of time. The author has known of instances where wrought-iron pipes and galvanized boilers could be used only four or five years before being made entirely unfit for use, the pipes becoming almost completely filled and the boiler rusted through.

On the other hand, he has seen galvanized supply piping taken out that has been in use for twenty to thirty years, which was very nearly as clear as when first installed.

When pipe is to be laid underground, and the quality of the water will possibly permit, it should be lead rather than wrought iron, as the former has a much longer term of life when subjected to the corrosive influences incident to the moisture of the ground.

For this reason, service pipes, even though of wrought iron, are usually connected to water mains by means of lead connecting pieces. Such connections are to be seen in Fig. 248. The upper

connection made without lead is wrong, for it is very rigid, and liable to be broken off, whereas the lead connection will give sufficiently to take up any such strain.

From the lead connection the service pipe is carried to the