Leaks are insidious because the water disappears into the ground rather than appearing somewhere obvious. The evidence is usually indirect — vegetation, ground condition and smell.
Long-running leaks wash soil fines away from under the pipe and, in the worst cases, from beside foundations, which is a subsidence risk worth taking seriously.
Confirming a leak needs testing, not guesswork: a camera survey to find suspect joints, then a water test or dye test on the suspect section.