About 2 years ago, I heard water running through my bathroom pipes as well. It turned out to be a broken pipe under the street outside my house. I ended up paying a lot for water charges even if the water wasn't being used in my home. Now, I hear the same thing. I checked with DEP. They say it's nothing but the water meter propeller keeps turning even if all the water is shut off in my house. There's no leaky toilet, no leaky sinks, etc... The only thing I can think of is there is a small copper run-off pipe dripping into my basement laundry sink. I think it's some how related to my water heater in the basement. In the past, I only remember it dripping. Now, it's a steady stream. What could this mean and what can I do about it? I don't want to be wasting water and I'd want to know if my water heater is about to give out too. Thanks

Sounds like your TPV is opening and is draining into the sink. Is the water hot? If so, it could be too much pressure on the house supply or a leaking TPV. Have the house water pressure tested, a test gauge at HD is $10. Screw it on the HW heater drain and slowly open the drain valve. Pressure should not exceed 60#. If you have pressure greater then 60, you can try and adjust the main valve by opening a tap and adjusting the regulator screw out a bit. If the pressure drops you may be OK. Otherwise, you will have to replace the main supply regulator. Now, if the pressure is 50-60, I'd replace the TPV. Shut off the house water, close the CW supply to the HW heater, turn off the gas or electric to the heater, open a HW tap on the upper floor, connect a hose to the HW heater drain and drain out about 20 gallons. You will probably have to cut the TPV drain pipe near the valve, unscrew the TPV-it might be very tight- and get a replacement, usually less then $15. Install the new TPV, put a 3/4/IP to 7/8 compression fitting on the valve and connect the drain back and tighten. That way, you can remove the TPV without cutting the pipe. Let us know what you find out.

Remind yourself to check your T&P valve twice per year. If it drips, there is a problem and it shouldn't be left alone like you have already done. Address any temperature and pressure related problems. If house pressure is 80 psi or above, have a regulator installed. If a regulator is already in, adjust it or have it replaced if it is non-operational. Add provisions for thermal expansion even if you only have a regulator, the TE bypass is not a sure bet to prevent thermal expansion in the water distribution system. Keep hot water tank temperature between 120 and 140 degrees Fahrenheit to reduce the amount of legionella bacteria proliferation.
Very simple preventative actions can save you a lot of problems in the future.

What's TPV? The water is cold. There's another pipe that looks the same with the same diameter (about the thickness of a pencil) and copper (?) coming off the cold water faucet of my laundry sink. This other pipe is curled like a telephone cord but not as tightly. More like around a soda can. That one doesn't have any water coming out of it.

What's the T&P valve? Where do I find it? Is it on the water heater already or is this something I have to add on? We keep our hot water tank at 120 degrees. It's also saved us some $ off our heating bill.

Temperature and pressure (T&P) relief valves used on residential water heaters are typically designed and manufactured to relieve on pressure at 150 psig and on temperature at 210 degrees F. These ASME, ANSI and CSA (AGA) approved relief valves protect the water heater from excess pressures and temperatures by discharging water, see the images below, Thanks.

John