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HEALTH AND SANITATION
Getting Ahead of the( Hunter’ s) Curve
By Matt Chapuran
David Viola, IAPMO CEO In the spirit of the sharing of unique experiences that shape the plumbing industries in our respective nations, the following article looks at projects that benefited from using IAPMO’ s Water Demand Calculator ®. Written by correspondent Matt Chapuran, it is the next in a regular series of similar articles that will run in this magazine.
Dave Viola IAPMO CEO
IAPMO’ s water demand calculator is proving its worth— in rands, dollars and better health outcomes— in projects from coast to coast.
Citing research that reached as far back as 1921, Roy B. Hunter wrote,“ It is hoped that this series of papers will supply the logical answer to many of the controversial questions pertaining to pipe sizes and design of plumbing construction.” But not content with such historic data, Hunter was leaning on the current research“ on plumbing for low-cost housing.”
From these origins were born the Hunter’ s Curve, which for eight and a half decades has estimated the required pipe size to accommodate a building based on the number of fixtures. Since 1940, the sophistication of fixtures, including low-flow toilets, has greatly reduced that demand, leading to oversizing of pipes, bloating of installation and maintenance costs, and public health concerns synonymous with oversized pipes.
“ How many other areas of modern life are still governed by thinking back from the 1940s?” asks Gary Klein of California-based Gary Klein and Associates, Inc.
In a 2024 presentation to the Los Angeles chapter of the American Institute of Architects Klein and IAPMO’ s Christoph Lohr asked audiences if they were aware that“ the formula from the 1940s for design flow rates assumes that every home operates like a sports stadium at half-time with queue lines to use fixtures”.
A refresh was ready. In 2017, IAPMO released the Water Demand Calculator as part of its Water Efficiency and Sanitation Standard( WE • Stand) and the Uniform Plumbing Code( UPC ®). Built on a Microsoft Excel platform. The Water Demand Calculator draws from 10 years of contemporary data, delivering benefits to a variety of project types in virtually all regions of the country.
One success story that Klein cites is Nueva Esperanza in Hillsboro, Oregon. Completed in 2023, the project’ s 12 buildings include 150 units ranging from studios to four-bedrooms, on a six-acre parcel. The project saved an estimated USD400 000 in capacity fees when local officials approved a two-inch water meter based on Water Demand Calculator( WDC) estimates, where Hunter’ s Curve would have recommended a four-inch meter.“ This affordable housing property suddenly got a whole lot more affordable,” Klein says.
www. plumbingafrica. co. za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline July 2025 Volume 31 I Number 05