There are several types of ...

There are several types of water loss, but the ones you pay for are perhaps the most important.  The fastest way is to find the water meters that enter the area in question.  Locate what they feed and read them at night when all good people should be fast asleep and not using water knowingly.  in the UK this is 0300hrs to 0330hrs, but it may be earlier or later depending on night activity.

On meters with high night use, identify if there is a reason for it.  There is a certain amount of domestic use at night but by the selecting time you choose it is likley that local cisterns could be full.  If these continue to fill throughout the night this will indicate a number of things, leakage being one of them,

There is a lot of references on the UKWIR website with a 'Manageing Leakage tome being quite the most comprehensive.  Get the college to buy it.   Good Luck