The WatSup™ (Watsup Model Systems Ltd) model is a high resolution model of dendritic water supply networks formed by interconnected modules. Each module, e.g. a house, office, etc, can have multiple users using elemental demands, which can be stochastic or deterministic, to produce representative flows. Elemental demands represent water using devices, e.g. a toilet, and are modelled as flow against time. Stochastic elemental demands have modeller defined variability and can include queuing. Deterministic elemental demands occur at fixed times. Modules, which can include local storage, are interconnected to form networks with the flows being aggregated at each node. Network and system faults can be introduced as stochastic processes, flow limits and hydraulic constraints are observed and queued demands carried forward until satisfied. A novel double sweep algorithm is used to distribute flows within the model. The WatSup model uses an advanced object-oriented numerical engine to provide a robust, fast modelling system with a time step of one second.