A leak in your house – no matter how small it is – can be one of the most worrying and potentially expensive things to go wrong. When it is under concrete things can get even worse because unless you can trace the approximate source of the leak you may have to start pulling up the entire floor, which can’t simply be replaced like floorboards. A leak under a concrete floor will have the pound signs flashing in your plumber’s eyes, but if you can find where the leak is coming from yourself, you may even be able to fix it.
Find the heat
Find the area of the floor that is warmer than the rest. Nine times out of ten it is your hot water pipe that will be leaking, so walk around with no shoes on. As funny as it may sound, if the cat has taken to sleeping on a new spot on the carpet, this could be your hot spot too. This technique is only really useful if the hot spot is new – if it was always there it is probably just an area where the pipe is closer to the floor than the other parts.
Lift up any carpet, lino or floorboards that are sitting on top of the concrete. Look for a wet patch or feel again for warm spots. If there is a wet patch, dry it up with towels, a heater or a dehumidifier, and then watch where the water returns. Again, this may not always give you the exact location of the leak as water can run down the outside of a pipe if it is only a small leak, so combine this technique with one or more of the others.
Use a stethoscope or another listening device to check for the sound of a leak. It will probably sound like stones being sprayed with water if it on the ground floor. Move around the floor to where the sound is loudest and this will likely be where the leak is coming from.
Use infared sensors or other thermal imaging technology to show exactly where the leak is coming from. You can call out specialists or hire the equipment, but this can be expensive. You will have to weigh up the cost of getting the sensors in with a plumber’s estimate. In some cases it is easier to re-pipe part of your system, bypassing the leaking pipe, so check.
Make sure there is actually a leak by turning off all the appliances that use water and looking at your meter. If it is still spinning, you have a leak.
Don't undertake any large jobs unless you feel very confident doing so.
Turn off the water at the valve before attempting to fix a leak.