Take a look and see if a toilet is running or a tap is dripping. If so, it might be your leak, and a good thing is to avoid spilling water, and enable monitoring of more harmful leaks. Try to close the main valve and see if the temperature reading off the pipe gets close to the temperature reading of the surrounding air.
If temperature reading of the pipe never reaches 3 °C of the reading of the surrounding air, your pipes are likely to have a leak.