How often do water supply lines or sanitary sewer lines leak?

As reported by the Austin American Statesman, during the hot drought period in 2011 in Austin, the Austin Water Utility via spokesman Jason Hill reported 55 calls a week average concerning broken (leaking) water lines.  The typical average during summer seasons is 35 to 40.  "A good portion of the ones we are seeing are the small lines from the water mains to the homes."  In 2009 40 to 60 leaks a week were reported in June, July, and August, with a peak of 66 in the last week of August.  In 20111 a high of 103 leaks was reported in the last week of July.  Another figure reported for 2011 was 60 to 80 per week.  October 2011 reported approximately 50 leaks per week.

Texas municipalities reported system leak rates in 2013 and the leak rate varied from 4% system wide loss to as high as almost 18%.  Water mains under residential streets can impact house foundations in the adjacent lots.  Leaks in the feeder lines to homes also contribute to the loss.

Back in the early 21st century when many geotechnical engineers were assisting insurance companies with homeowner's insurance policy claims related to house damage with a suspected cause being soil movement and plumbing leaks, hundreds and hundreds of claims were apparent.  Many of these claims did reveal plumbing leaks.

It is foolish to design site preparation and foundations based on the assumption that either (1) a plumbing leak will not occur, or (2) if a plumbing leak occurs well then the owner is out of luck.  This is ridiculous.  You do not design building foundations based on luck, particularly for a condition with a relatively high probability of occurrence.