Introduction. Acknowledgements. Notation. Important SI units. Basic conversion factors. Data management systems in water supply. Water supply at the millennium. Managing a water supply system. Data required for operational management. Data capturing system. Data management system. The dissemination of operational data. Analysis of operational data. The value of on-line data. Deciphering the message. The logic of data. Analysing the balance. The case for mathematical modelling. Modelling water supply system elements. Structure of a hydraulic model. Modelling real-life systems. Sources of water. Pipes and pipe networks. Service connections and public standpipes. Reservoirs. Pumping stations. Valves. Modelling of demand. Introduction. Definitions and terminology. Analysis of demand. Capturing, holding and converting data to information. Losses. Modelling demand. Mathematical methods applied in modelling. The principles of modelling. Computation of one steady state. Continuous stimulation. Initial state. Choosing adequate software. Making a model. The general approach to model making. Practical advice on model building. Solving difficulties and some common errors. Recognising typical solutions. First simulation runs. Calibration of the model. Modelling and real-life problems. Simulation models as tools for design. Modelling and operational management. The use of models in a water company. Modelling energy costs. Modernisation of control systems. Models and operational management - cases from real life. Leads for beginners. Appendices. References. Glossary. Index.