Written by IAPMO 8:44 am Code News, IAPMO News

Updating Hunter’s Curve: The WDC Summit

Let’s Make History Together

Plumbing engineers and designers have been talking about it for what seems like forever. Plumbing installers have been looking into ways to become more efficient. Plumbing manufacturers have been collecting the data to better size their equipment. And plumbing inspectors and plan reviewers have been acutely aware of the need for change for a long time. Of course, anyone in the plumbing industry knows that what I am talking about is Hunter’s Curve. In the U.S. plumbing industry, there has been widespread consensus that we have been oversizing our domestic water systems for decades. While the work that Roy Hunter completed in 1940 was revolutionary for the time, we all agree that it is well past time to update the way we size these systems. 

Most of the plumbing engineering industry is already aware that IAPMO, ASPE, and the University of Cincinnati collaborated to create the Water Demand Calculator — also known as the WDC — and that the WDC ultimately was added to the 2018 Uniform Plumbing Code (UPC) as Appendix M. This marked the first time in almost 80 years that an alternate to Hunter’s Curve pipe sizing methodology was added to a model code. The benefits were quickly apparent as Stantec identified in their report:

  • Up to 11% cost savings on copper piping (based on pre-pandemic material costs)
  • Up to 16% cost savings on PEX piping (based on pre-pandemic material costs)
  • Improving water quality by reducing water dwell times
  • Faster hot water delivery and improved energy efficiency
  • Less water stored inside plumbing systems can help improve water conservation efforts

Additionally, the Alliance for Water Efficiency (AWE) completed a study showing the incredibly positive economic impacts to home builders that reduced utility/water-meter connection fees had as a result of utilizing the WDC.

The only drawback? The WDC is meant to be applied only to residential buildings, either single or multi-family (such as a high-rise condo/apartment). Offices, hospitals, schools, restaurants, and other non-residential commercial buildings still need evaluation. That’s where the WDC Summit comes in: to kick start a movement. A movement that needs YOU!

On Nov. 1, 2022 IAPMO and ASPE are hosting a second virtual summit. “Updating the Hunter’s Curve: The Water Demand Calculator Summit” will be the second step in taking the WDC and applying it to all other building types over the upcoming years. In the short-term, however, this will be a great event where participants can learn about Hunter’s Curve and how it was developed, comprehend how the WDC works, and understand what steps are needed to replace our 80-year-old sizing methodology for most commercial buildings. These educational seminars will offer 0.6 CEUs (or 6 PDHs). Additionally, there will be a 1-2 hour panel discussion that will be open to all attendees to provide comments/questions and join in the dialogue. Cost to attend the summit will be $49 — this is in part to make sure all attendees have “skin in the game” into making the event a success. 

In the 21st century, social movements have shifted away from being top-down. Instead, positive changes are often crowd-sourced. Grassroots initiatives are key in making changes, and it likely will be no different for our industry to update Hunter’s Curve. This is the opportunity to “crowdsource” the development of an updated “Hunter’s Curve” for which our industry — engineers, installers, inspectors, etc. — has been clamoring. In this sense, the WDC Summit is only the project kick-off meeting. After the summit, participants are encouraged to join the Water Demand Calculator Task Force, which will be expanding. (If you want to volunteer for the task group you don’t have to attend the summit — although we would love to have you do both!) Engineers can volunteer their time. Manufacturers can volunteer their data. If you have data or time that you can donate, we would love to have you be a part of this movement. All of us can be part of history. In this effort, we can make history together. 

I’d be remiss if I didn’t add the final benefit to becoming involved in this crowdsourced effort: the opportunity to have your name “etched in history” as it were. I’m sure many of you are like me when driving around your home city; you’ll point out buildings to you children, your significant others, your friends, and say proudly, “I worked on that building.” We take pride in what we do. We make a difference in society by impacting public and health and safety through our God-given talents. This initiative takes that occurrence to the next level: this is like-minded professionals, working hard together to achieve a purpose outside of ourselves, making history together, impacting ALL of society.

This would be going from Hunter’s Curve to a “Plumbing Industry’s Curve” — something we can all be proud of. If we make this happen together, no longer will we just drive around telling our loved ones we worked on such and such building — rather we can say with confidence we made an impact to our city, state, and country as a whole. We could, in theory, point to every building under construction and say, “I had a part in that.” And we could tell our loved ones that we worked on a project that had a purpose outside of our day-to-day work.

So, come and attend the WDC Summit. Listen and learn. Add your voice to the conversation. And then volunteer to make a difference. 


IAPMO develops and publishes the Uniform Plumbing Code®, the most widely recognized code of practice used by the plumbing industry worldwide; Uniform Mechanical Code®; Uniform Swimming Pool, Spa and Hot Tub Code®; and Uniform Solar Energy, Hydronics and Geothermal Code — the only plumbing, mechanical, solar energy and swimming pool codes designated by ANSI as American National Standards — and the Water Efficiency Standard (WE-Stand)™. IAPMO works with government, contractors, labor force, and manufacturers to produce product standards, technical manuals, personnel certification/educational programs and additional resources in order to meet the ever-evolving demands of the industry in protecting public health and safety.

Last modified: December 30, 2022