These, therefore, must be put in order with care and despatch. The underground portions, not being subjected to either heat or frost, are less liable to injury. Defects are either of the sort that can be remedied without stopping the flow of the water, or such as cannot be made without diverting the flow, as, for example, those which have to be made in the channel itself.
These latter become necessary from two causes: either the accumulation of deposit, which sometimes hardens into a crust, contracts the channel of the water; or else the concrete lining is damaged, causing leaks, whereby the sides of the conduits and the substructures are necessarily injured. Sometimes even the piers, which are built of tufa, give way under the great load. Repairs to the channel itself should not be made in the summer time, in order not to stop the flow of water at a time when the demand for it is the greatest, but should be made in the spring or autumn, and with the greatest speed possible, and of course with all preparations made in advance, in order that the conduits may be out of commission as few days as possible. As is obvious to every one, a single aqueduct must be taken at a time, for if several were cut off at once, the supply would prove inadequate for the City's needs.
Repairs that should be executed without cutting off the water consist principally of masonry work, which should be constructed at the right time, and conscientiously. The suitable time for masonry work is from April 1 to November 1, but with this restriction, that the work would best be interrupted during the hottest part of the summer, because
