go to your water meter, observe the running numbers.
dont use water at home for 30min, come back see again.

if numbers increase, means you got clean water leak.
repeat the test by switching off parts of your incoming, eg to toilet

if number no increase, means is dirty water leak. can be toilet, sink seals fail.

in both case, need to call in plumber.

if your house pipes are blue ABS, no need to investigate, straight change whole house pipe.

blue pipes is ABS. aku break sendiri

when the contractor come, ask them to quote for whole house replacement. pain one time.
you can go for pvc or copper