Modeling water consumption and flow rates for flushing water systems in high-rise residential buildings in Hong Kong

The probable maximum flow rates and flushing water consumption of a residential development are two crucial design factors for flushing water plants and evaluation of the risk of overloading them. Flushing water demands are transient and influenced by occupant load variations, occupant usage patterns, installed appliances and system commissioning. This study proposes mathematical expressions to determine the water consumption and flow rates for flushing water systems of residential buildings in Hong Kong. The model parameters were identified from a recent survey on the water closet (WC) usage patterns of 14 high-rise residential buildings. The occupant load factor, diurnal variation of flushing, discharge and refilling durations and volume of the WC cistern recorded from 597 households were used to determine the uncertainties of consumption and flow rates, and hence the risk of overloading a plant. Predictions were made for two typical residential buildings in Hong Kong. Good agreement between the predicted and the measured flushing water consumption was found. This model would be useful in calculating the capacity of a flushing water plant and the associated risk of overloading it.