Water companies may read the meter as often as every month or as infrequently as every year or two. In general, larger water companies may choose to take readings at six-month or yearly intervals, but small companies read meters more often.
If water readings are not performed once per month, the monthly bills that customers receive may be estimates. These estimates are generally based on average usages from previous years. When the meter is read at the end of a six-month or year cycle, the total charges are added up, and the next bill may contain an adjustment to account for differences between the averages and actual usages in the previous cycle.