Optimising water demand estimation in non-residential buildings: A new design flow rate approach

Accurate estimation of water demand in buildings is essential for designing safe, efficient, and sustainable water supply systems. Conventional design approaches often lead to significant overestimations of water demand, resulting in water supply systems that are frequently oversized. This study introduces the Water Demand Estimation Model (WDEM), a novel stochastic model developed specifically for application to non-residential buildings. The model integrates statistical data on sanitary appliances and user behaviour using extensive Monte Carlo simulations to generate realistic scenarios of simultaneous appliance usage. In addition to appliance properties, WDEM accounts for building occupancy, an essential factor in design flow rate estimation. It provides a set of user-friendly design equations, as an essential step towards future application in practice. Application of WDEM to three diverse case study buildings revealed substantial reductions in estimated design flow rates, ranging from 63% to 73%, compared to current UK design guides. These findings demonstrate WDEM’s effectiveness in estimating water demand and thereby avoiding system oversizing, which is crucial for designing water supply systems that are cost-effective and have improved water quality. Practical application The WDEM provides a new approach to estimate water supply design flow rates by combining occupancy-based usage with appliance-efficiency ratings to derive explicit design equations. The outcomes include preliminary design equations which, once validated, should support improved estimation of design flows without running the simulation. In practice, WDEM may support faster early-stage decisions, potentially smaller pipework and storage volumes, reduced capital costs and pumping energy, and lower stagnation and water quality risks.