IAPMO Water Demand Calculator

We Did the Math: Right-Size Plumbing Pipes to Reduce Construction Costs and Address Water Aging

The IAPMO Water Demand Calculator is available from the Apple App Store for Apple devices and Google Play for Android devices.

Google Play Store App Store

It may sound hard to believe, but plumbing systems in new home construction are routinely overbuilt because the most commonly-used pipe sizing formula is almost 90 years old.

Excessive construction and meter connection costs are just the beginning. Oversized pipes just don’t work as well with today’s high-efficiency fixtures and appliances.

Hot water taking too long to get to your shower? Large-volume pipe diameters cause hot water delivery delays to low-flow fixtures. Even worse, there risks for water-borne pathogens from water aging and stagnation in residential water pipes.

It is time to update the math behind plumbing pipe sizing.

The IAPMO Water Demand Calculator is the first statistically-based update to Hunter’s Curve. Hunter’s Curve is the formula plumbers have used to calculate peak water demand usage in single-family homes since the 1930s. Using the IAPMO Water Demand Calculator instead of Hunter’s Curve can provide as much as a 65 percent reduction in water demand estimates, meaning:

  • Home builders will realize a 1x to 3x pipe size reduction in the water service line, depending on the home’s size. It can save hundreds and even thousands of dollars on lower water service connection fees, as well as meter and pipe costs.
  • Homeowners with right-sized pipes will spend less time waiting for hot water, reducing water and energy waste, as well as frustration.
  • Accurate pipe sizing means better water quality, mitigating the growth of pathogens such as Legionella.

The IAPMO Water Demand Calculator works in conjunction with commonly accepted rules and procedures for sizing cold and hot water systems.

IAPMO provides the Water Demand Calculator as a free app or spreadsheet download to facilitate rapid adoption and improve new home plumbing systems for everyone. IAPMO continually invests in research to help communities benefit from today’s sophisticated water-related technologies in our homes and buildings.  It’s one of the ways we play a vital public health role in assuring access to clean water and sanitation.