Abstract
A conceptual end use model for residential water demand and return flow is presented in this thesis.
The model requires a unique description of a single residential stand in terms of all its end-uses.
The end-uses include toilet flushing, bathing and showering, garden watering, leaks, et cetera.
Various parameters describe each of the end-uses. The model predicts five components relating to
water demand and wastewater flow at a residence: indoor water demand, outdoor water demand,
hot water demand, wastewater flow volume and concentration of solutes in the wastewater. Twelve
monthly results are calculated, for each of the five components, to provide a typical seasonal
pattern as well as an annual value.
The large number of input parameters in an end-use model allows for powerful and detailed
analysis. The parameters required to populate the model are discussed and guideline values are
presented.
The end-use model is used to conduct a sensitivity analysis of each independent parameter for
each of the five individual model components. The elasticity and sensitivity is determined at a base
point with respect to each parameter for all five results. A research significance index is also
devised to integrate the elasticity and availability of data for each parameter. The result is a
prioritised list of the most critical parameters for each of the five components, which are the ones
that should receive the focus for future study and data recording.
The parameters are combined to obtain a list of the overall most important parameters in the model
for all components combined, and based on a combination of the elasticity-based rank and the
sensitivity based rank. The five most important parameters are the household size, toilet flush
frequency, toilet flush volume, the washing machine event frequency and the volume of leaks on a
stand.
The practical application of the model is illustrated. The researchers first apply the model to mimic a
few commonly accepted characteristics of water demand. The effectiveness of some specific water
demand management measures are evaluated by adjusting selected model parameters. The
measures include xeriscaping, the installation of dual-flush toilets, low-flow showerheads, pool
ownership and pool cover use. The model also enables practitioners to obtain an insight into the water use habits of homeowners.
The model forms the basis for further research work in the field. Its relatively simple structure and
realistic data requirement encourages its integration into existing commercially available software
suites for water and sewer system analysis and -management in the civil engineering industry in
South Africa, as well as abroad.
Prof. J. Haarhoff