Bills change according to water usage, which fluctuates as a result of a number of things, including the number of people who live at a property. Everyone has different personal water habits that will affect the amount of water used in a given month, and water consumption may vary from season to season. Many customers increase their water consumption in the summer months by using water cooled air conditioning, watering gardens, washing cars, filling swimming pools, etc. Bills may also fluctuate based on the number of days in a billing period. The City of Troy bills quarterly, however, on occasion a bill can be over or under the 90 day period. Most bills are based on actual readings, while estimated bills are based on usage history.