Prioritisation of parameters influencing residential water use and wastewater flow

A residential end use model (REUM) which accounts for indoor water demand, outdoor water demand, hot water demand, wastewater flow and the mass of total dissolved substances (TDS) in the wastewater, was earlier described by the authors. The integral relationship between water quality and quantity in the model allows for holistic modelling of different water demand management measures' effects. The model covers 16 independent micro-components of water use and requires numerous model parameters. This paper has the objective to prioritise the 79 parameters which remain after stripping all possible redundancy from the model in terms of their relative impact. Two ranking criteria are used: the elasticity and the sensitivity of each parameter. The results, benchmarked to a typical South African suburban residence, show that household size is the most notable parameter for modelling the indoor water demand, hot water demand and wastewater flow volume. Pan evaporation and a factor describing actual lawn irrigation in relation to theory are most notable for modelling the outdoor demand. Wastewater TDS concentration is dominated by what is added at the toilet rather than pharmaceuticals and personal care products (PPCPs) added at other entry points to the wastewater system. The methodology developed and results obtained underpin the view that effective water demand management policies can only be rationally formulated with the assistance of a comprehensive water and wastewater model based on micro-components of water use.