Traditional water distribution modelling theory gives primacy to demands over pressures, thereby making demands the fixed and independent input variable, and pressures becoming the dependent output variable. This approach is very convenient for systems without any pressure limitations so that demands are always met. However for pressure-constrained systems the models do not give sensible results as they do not demonstrate the fact that with declining pressures, flows will also correspondingly decline in reality. In order to carry out more realistic modelling, it is important to divert from the traditional demand-driven approach and inculcate methodologies that recognize the relationship between flow and pressure, also called the head-driven approach. This paper applies both methodologies to an intermittent water supply system and demonstrates that in cases where pressures are insufficient, traditional demand-driven models should be substituted with head-driven models.

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Technical Paper