Smart water-meter networks are more and more often implemented in Polish water supply systems. They include all water meters of recipients and their indications are saved every hour. This solution makes it possible to calculate real water consumption, estimate minimal authorised water usage for DMA and the whole town and calculate real water balance and water loss. However, the number of records (above 66 of millions yearly), communication problems and wrong/missing water meter indications can lead to serious mistakes in water balance. Therefore critical approach to records is the key element of water balance. The paper shows selected possibilities and problems of maintenance of Advanced Metering Infrastructure (AMI system, about 7600 water meters) in a town with 46 000 inhabitants.