Your bill varies from month to month for a few reasons. The first reason your bill varies is due to the seasons. Summer heat generally increases the usage of air conditioners and water. Colder months usually see an increase due to heating requirements, longer nights, and the longer usage of lighting.
Another reason you bill varies is the number of days between meter readings. (which is indicated on your bill). We try to keep the billing period as close as we can to 30 days; however, holidays and weekends come into play occasionally resulting in a longer time frame.
Other things that can affect your bill are extreme weather, leaks, malfunctioning appliances, as well as problems with your HVAC unit or water heater.