For the hot water system brass pipes are to be used as they are not affected by the alternate warmth and chill of the water, which would cause lead pipes to sag between the supports. Indeed, if the additional expense is not too great, it will be worth while to make all the supply pipes of brass, which can be obtained either plain or coated inside with tin. If brass piping is used it must be put up so that the angles and bends are free to move a little, or the expansion and contraction will strain the fittings and produce leaks. The effect which the water will have upon the pipes is a matter which should be considered, but can only be determined by local examination, and recommendations as to the use of piping must be made with reference to the analysis of the local water supply. If brass piping is used it should be semi-annealed and specified as "iron size", that is, the thickness must correspond to that of iron pipe of similar size, as distinguished from so-called "plumbers tubing", the use of which is not to be recommended.