Does insulating hot water pipes save electricity?

May be. February's electric bill was $104, down from $141 in January. Both months were cold. I've been gung ho on turning out un needed lights. The only thing I did differently in February was insulate the copper pipes running to the water heater. Used to be, the pipes were hot to the touch all the time, a sign of expensive heat leaking out of the heater thru the copper. I bought a $4 pack of plastic foam insulation sometime in January and snapped it over all the exposed copper pipe. If true, this makes a $37 monthly saving from a $4 investment. Something dropped my usage from 940KWH in Jan to 697KWH in Feb. Price didn't change, I'm paying $0.15 per KWH in both months. For this month's magic energy saving trick I'm going to insulate the big hole that runs my electric wires from the junction box into the sills of the house.