If you receive a notice from NWP saying your bill for last month was 0, there's a good chance the batteries are dead in the sending unit in your water heater closet. This must not be ignored since NWP charges hundreds of dollars for a service call. Just replce the two AA batteries, per this video.
If you don't have time to watch, it's just a matter of prying open the little plastic box hanging on the wall in your water heater closet. The batteries point in different directions when correctly installed. Be sure the male end of each battery points to the plus sign. Again, one battery points up, the other down.
