The meter stops when the water tank supply valve is closed.
If so, there is a leak in the water tank itself or in the pipes after the water tank. Check for leaks in the water tank first, and if there is no problem, you should look for leaks in the pipes after the water tank. The pipes after the water tank can be considered as one connected pipe, but since you cannot inspect the entire pipe at once, it is good to be able to divide it into sections. It is important to check if there are any shut-off valves on the premises.