In water management the maintenance of water systems is essential. The actual condition of each component has to meet the requirements of safety and operational performance. As a consequence, the actual conditions of the water system have to be monitored continuously to gain insight into necessary maintenance. Up till now, traditional maintenance methodology meets the needs concerning execution of maintenance works but does not meet the needs for rational planning and budgeting for the maintenance activities. Therefore, a decision support system for rational planning and calculation of maintenance of water systems has been developed. Several test cases have been carried out.