A flushing water consumption model for residential buildings in Hong Kong

Domestic water closet (WC) flushing consumes a considerable amount of the total water supply in a typical apartment; however, there is a lack of concern about the consumption of flushing water due to occupant load patterns in cities having a high population density, e.g. Hong Kong. Indeed, flushing water consumption is of primary importance in designing a plumbing and drainage system for buildings. This paper proposes a mathematical model of flushing water consumption for residential developments. Density functions of the model parameters, including the installed cistern capacity and usage patterns of water closets, occupant load and its diurnal variations, were determined from a recent survey for water consumption in some residential buildings in Hong Kong. In particular, numerical values of the parameters were sampled from the density functions using the Monte Carlo technique in order to determine the probable flushing water consumption for a residential development. The model accuracy was verified by the measured flushing water consumption in a residential building. The results showed that occupant load and its variations had significant influence on domestic flushing water consumption and that confirmed the highlight of the proposed model. The model would be a useful source of reference in determining domestic flushing water consumption for residential building developments with appropriate model parameters selected. Keywords Occupant load, Water consumption, Residential building, Water closet