You may want to turn everything off in the home, and then check the meter to see if there is any movement of the numbers. Sometimes there is a little dial that spins if water is running.
If the water in the shower goes "up" when cold is being used, that just means that the pressure has dropped on the cold side, and the hot isn't being compensated for. Newer valves have pressure balancing.
An electric water heater will recover at about gallons per hour.