I hear water running every 7 to 8 minutes for about 3 seconds at a time this happens 24/7, it's not coming from any of my bathrooms and there is no water anywhere including around the water heater but i hear it at the water heater which is 19 years old and is being replaced Tuesday, where could the water be leaking unseen???

Best guess is a toilet leaking so that the fill valve comes on from time to time.

Try dumping some coffee of food dye in all toilet tanks without flushing for 10 minutes then check to see if the water color in the bowl changed... if using coffee make sure its brewed do not put coffee grinds or beans in the tank

You probably have a toilet that is "phantom flushing". A little water leaks out of the tank and the fill valve kicks on for a few seconds to fill the tank back up. i It's probably a flapper or flush seal that needs to be replaced. The toilet may not run at the exact moment you check it. Shut off the water to one toilet at a time to determine which one is the culprit. Good luck!