First you can hire a leak detecter to tell you where is leaking or you can do it yourself.
1. shut down all the facut and valve, includ the one for the hot water tank.
2. if there is a leak, than it is cold water line.
3. if there is not a leak,than turn on the valve for the hot water tank,if you see the meter is turning, then it is the hot water line leaking.
4. it is way better to ran new pipes from above in stead of dig up the pipe from the concret.
good luck
