Because the meter reading continually increases from the time the meter is installed, if there is a reading erroror if the computer estimates a reading incorrectly, the bill will always correct itself on the next reading. If for example the computer estimated high, the difference from the previous bill and the estimate would be high and you would get a larger bill than normal. The next time the meter is read the calculated consumption will be lower because it would be the differencefrom the high estimate and the current reading. Your next bill would therefore be lower, making up for the earlier higher bill. Water meters are usually very accurate.
Water going through the meter turns a propeller device which turns the meter.
If you think your meter is inaccurate you can have the meter tested by calling public works. A fee is charged for meter testing, which is returned if the meter is not accurate.