Modification of Hunter’s Curve in the Perspective of Water Conservation

Plumbing-system designers, who routinely use Hunter’s curve for estimating domestic demand, actually solve complex problems based on the probabilistic approach. Recently, serious questions have arisen about the accuracy of Hunter’s curve. In some instances, using the curve to estimate the water-demand load has given highly inflated results. However, this consistent problem in applying the curve to design should in no way be interpreted as a criticism indicating that Hunter’s basic research and approach are incorrect. Many things have changed since 1940 when Roy B. Hunter’s BMS65 Methods of Estimating Loads in Plumbing Systems, was published as a national standard in the United States. In the context of water conservation, which should be the primary goal in the global water-stressed scenario, designers are giving importance to using low-water-use (demand) fixtures. Merely recommending the use of low-water-flow fixture cannot address the issue of water conservation. Hunter’s curve was based on 1940 high-flow fixtures with a very high confidence level (CL) of 99%. Hunter’s curve needs to be modified in this context. In the present study, to obtain the optimal water demand of the plumbing system, Hunter’s curve has been modified by incorporating low flow rates of modern fixtures, the reduced probability of a modern fixture being on at any moment, and reduced CL in the binomial probability function as used by Hunter. Low-flow fixtures will be meaningful when the demand calculations must also address the issue of water conservation, and in this context, this paper’s modified Hunter’s curve will address optimal design of plumbing systems thereby facilitating the conservative and sustainable use of water.