I have a clearly audible hissing (leak type) sound in the area of my upstairs bathtub. It seems loudest when placing my ear to the wall behind the tub.

When turning off the water supply to the hot water heater, sound still remains.
When turning off the water supply at the curb, the sound disappears.
When the water meter is on and all home water is unused, the meter still spins (i.e. I am certain we're losing water)... the bill is also noticeably higher.

It has been getting worse over the past couple weeks (louder sound), but there is absolutely NO evidence of water or water damage ANYWHERE! (possible exception... the side yard *might* be a bit more moist than usual.

Any idea what may be causing this or how to determine the location without tearing apart the entire house?

Thanks for any advice you could give.

P.S. I had a plumber come by this afternoon (who didn't seem super duper bright) and said it's a leak under the slab and would need a reroute from one manifold to another manifold to bypass the line leaking under the slab. My problem with this is... The sound is quite loud in the upstairs bath, but when downstairs, you can only hear it emanating from above. I cannot comprehend how a leak under the slab could be so loud at ONLY the upstairs bathtub. HELP!!! If you help me locate and understand it.

I'm certain I can fix it, but not if I cannot determine where the problem lies.



Edited 2 times.

Does your house have a swamp cooler or humidifier? Is the wet yard near the bathroom(s)? I think it would be extremely rare to have a sizable interior second story leak and not show some damage somewhere in the interior.

Have you checked the toilets for leaky seals using food coloring or dye tabs in the tank
If it was an active leaking domestic water line in the house water damage would show
Do you have a crawl space?

If you turned off hot water heater inlet valve, and nothing is being actively used inside the house, that seems to suggest you have a cold side usage/leak.

Usages on the cold side can be unattended or unintentional, such as a toilet flush valve leak from the tank into the bowl slowly but steadily. It could also be a drip in an outdoor faucet that went unnoticed, or an irrigation system where the controller or solenoid have gone bad and partially leaking water outside underground, or the icemaker is filling water just at the moment you listened. I have even seen folks leave a garden hose connected to a hose bibb and leave the bibb on, only use the trigger on the nozzle to turn on or off, and the hose is coiled up on a rack against the wall, and a small puncture goes unnoticed for weeks. To eliminate all these I would suggest turning off ALL shutoff valves inside the house - toilets, lav sinks hot and cold, kitchen sink hot and cold, icemaker, dishwasher, washing machine hot and cold, and walk outside and disconnect all garden hoses from hosebibbs and make sure all hose bibbs are off. Check the meter again after that if you still have the dial spinning than you probably have a leak somewhere.

Also the sound of the hissing may not be where the leak is. I had a leak once when I heard hissing at night after I went to bed at midnight, got up to check and turned out the guy who I hired to paint the house did not turn the hose off, water was running out of the hose from 4pm to 12 midnight and flooded the alley, the hose was at the other end of the house, I was hearing the hissing in my bedroom because it was closer to where the pipe enters the house.