Pressure dependent network water quality modelling

Water quality models are increasingly being used routinely to help ascertain the quality of water in drinking water distribution systems for design and operational management purposes. Conventional water quality models are demand driven and consequently do not incorporate the effects of any deficiency in pressure on the water quality throughout the distribution network. This paper assesses a new integrated pressure dependent hydraulic and water quality model. The model is an extension of the well-known EPANET 2 model that has an embedded logistic pressure dependent nodal flow function. Hydraulic and water quality analyses based on two water supply zones in the UK were conducted for a range of simulated operating conditions including normal and subnormal pressure and pipe closures. It is shown that operating conditions with subnormal pressures, if severe and protracted, can lead to spatial and temporal distributions of the water age and concentrations of chlorine and disinfection by-products that are significantly different from operating conditions in which the pressure is satisfactory. The results here may be indicative of modelling errors that may not have been recognised explicitly hitherto.