The water has to go out somewhere, it can't just disappear. Start with the primitive means. Open sewer manholes and inspect for a fresh soil/sand into and abnormalities in the waterflow. Then try to find any soil anomaly along the water main route using a probe rod.
I have been told with quite common survival stories of people getting into a hidden death trap due to leak from underground pressurized mains transporting water in production sites. I have witnessed how a large autotower with a painter into it almost got tapped over by major sudden collapsing of asphalt paving underneath.
This is the reason why most users I am familiar with prohibit such piping - eventually they had to reroute those aboveground.
Edited by shvet1, 04 October 2024 - 06:38 AM.