设计一个水表计费系统，用于保存所有用户的用水信息以及水费余额。

若余额不足有相应提示信息。其中用户的用水信息记录为：编号、用户地址、户名、上次读数、抄表读数、水费余额。

-Design a water meter billing system, used to save all users of water as well as water charges balance. If the balance is less than the corresponding message. Water records: ID, user address, user name, and the last reading, meter readings, water charges balance.