136 LEAKAGE FROM STREET MAINS 



Well-made joints and careful caulking by skilled caulkers 

 are of the first importance. Testing pipes for leakage before 

 backfilling is one of the best ways of educating caulkers, and in a 

 system where the pipes are ordinarily so tested the caulkers will 

 learn to make joints that are always tight. 



There are several variations in the type of joint and in the 

 materials that are used in making it, and there are possibilities 

 of improving these. These matters, however, cannot be dis- 

 cussed in this place. 



In an old system of pipes there are bound to be many leaks 

 underground. Most of these leaks are so small that it will not 

 pay to spend the money to locate them and to dig up the pipe and 

 to correct them by caulking or otherwise; but there are also many 

 larger leaks and it is frequently possible to locate some^of these, 

 and the water that may be saved by stopping them is well worth 

 the cost. Some of the largest leaks will show at the surface of 

 the ground, but there is a great difference in systems in this 

 respect. If the soil is clayey and impervious, even a small leak 

 will force its way to the top and will make a wet place that can 

 be detected by one who knows the significance of such a spot. 

 On the other hand, with a dry gravelly soil, large quantities of 

 water may be lost without showing at the surface. 



This is one of the reasons for differences in leakage in differ- 

 ent systems, and it is not to be expected that quite the same 

 degree of tightness will be realized in pipes laid in an open 

 pervious soil as in an impervious one. 



Looking for leaks in an old pipe system is ordinarily best 

 carried out during the time of minimum consumption, that is, 

 between the hours of one and five a.m. In a strictly residential 

 community, the figures obtained at this time are a very good 

 index of existing conditions. If there are industrial all-night 

 users, the night figures are of little value. 



The underlying principle of test is to let the water supplying 

 the whole system or some part of the system go through a water 

 meter and to shut off parts of the pipes that are supplied in de- 

 tail and observe how the rate of flow is affected. In this way a 

 measurement of the whole minimum night flow for the district is 



