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If you’ve been in plumbing engineering for more than a minute, you’ve probably seen this before: systems sized with the best of intentions but the worst of assumptions — typically built on legacy models that were innovative for their time but now feel outdated. For decades, we’ve accepted oversized piping, stagnant water, and high installation costs as “just how it’s done.” But what happens when we stop guessing and start measuring?

That’s the kind of question driving IAPMO’s recent efforts to significantly expand the plumbing industry’s research infrastructure — efforts that, in my view, signal a much-needed transformation in how we think about water demand, system design, and public health.

This article takes a deep dive into how IAPMO is bringing new research capabilities to life through three interconnected efforts: the Water Demand Calculator®, the Innovation and Research Fund, and the integration of the Environmental Science, Policy and Research Institute (ESPRI) into IAPMO.

Each move represents a deliberate shift toward evidence-based practice — and together, they offer a vision for a future where science and codes are no longer separate worlds.

The Water Demand Calculator: A research-driven shift in plumbing design

In plumbing engineering, we often work within design paradigms handed down through generations. One of the most entrenched has been Hunter’s Curve — a 1940s-era statistical model developed to estimate simultaneous water demand and size water piping systems accordingly. It was innovative for its time and became the foundation of plumbing design for decades. However, much has changed in the built environment since World War II.

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Modern fixtures are far more efficient. We have a greater understanding of varied usage patterns, driven by a better understanding of behavioral changes, energy conservation mandates, and evolving building technologies. Perhaps most importantly, we now face greater awareness and urgency surrounding water safety issues like Legionella. These changes challenge the long-standing assumption that “bigger is better” when it comes to pipe sizing.

Oversized plumbing systems may look robust on paper, but in practice, they contribute to higher installation costs, longer hot water delivery times, increased water age and elevated energy consumption. All of these factors introduce risks — financial, operational, and public health-related — that modern plumbing engineers cannot afford to ignore.

From assumption to evidence

This growing disconnect between theory and real-world conditions led IAPMO to ask a deceptively simple question: Are we oversizing our water pipes?

To find a better path forward, IAPMO initiated work in 2013 as part of a multi-organizational effort with the American Society of Plumbing Engineers (ASPE) and the University of Cincinnati to create the Water Demand Calculator — a tool grounded in actual residential fixture usage data. Unlike Hunter’s Curve, which relies on theoretical peak usage rates and fixture unit multipliers, the Water Demand Calculator uses probabilistic modeling to more accurately estimate peak water demand based on how people actually use water today.

Derived from detailed studies of more than 1,000 households, the Water Demand Calculator generates pipe-sizing guidance that’s both practical and performance-optimized. The benefits are tangible:

• Reduced pipe sizing, resulting in lower material and labor costs
• Faster hot water delivery, enhancing occupant satisfaction and reducing water waste
• Shorter water stagnation times, lowering the risk of microbial growth such as Legionella
• Decreased energy consumption, supporting energy efficiency and decarbonization goals

This tool — now adopted into multiple U.S. plumbing codes — represents a shift away from tradition-bound design toward a new era of evidence-based engineering.

Advancing the science: Commercial building application

Having proved its success in residential applications, IAPMO has now set its sights on a more complex frontier: extending the Water Demand Calculator to commercial buildings.

Office buildings, schools, hospitals, and hotels present a far more diverse and dynamic set of usage patterns. That complexity demands a more refined data set. IAPMO is collecting field data from a variety of building types, tracking real-time fixture flow rates and behavioral usage patterns across different occupancy levels and daily cycles.

The aim is to develop a robust commercial version of the Water Demand Calculator that can provide accurate peak demand predictions for a range of non-residential structures. If successful, this tool could have far-reaching implications:

• Smarter system sizing in large-scale and mixed-use infrastructure
• Optimized energy and water use, reducing environmental and operational costs
• Improved hygiene and water quality, especially in facilities with vulnerable populations

This effort is about more than efficiency — it’s about futureproofing our plumbing infrastructure with scientific rigor and public health in mind.

A model for the industry

The Water Demand Calculator is a textbook case of how data can drive innovation in plumbing system design. By grounding our tools and standards in observed reality rather than outdated assumptions, we unlock opportunities for smarter, safer, and more sustainable buildings. As IAPMO continues to invest in research and real-world data collection, the Water Demand Calculator stands as a symbol of what’s possible when we ask bold questions and follow where the data leads. For plumbing engineers, it’s not just a new tool — it’s a new way of thinking.

Investing in discovery: The innovation and research fund

The Water Demand Calculator may have set a new benchmark in plumbing design, but its success is no accident — it’s the product of years of deliberate investment in data, modeling, and applied research. Recognizing that breakthroughs like the Water Demand Calculator are only possible through sustained support for scientific inquiry, IAPMO took a major step forward in April 2024 with the launch of the Innovation and Research Fund.

This fund represents more than just a financial mechanism — it reflects IAPMO’s evolution from a code and standards organization into a research hub for applied water science. The Innovation and Research Fund is designed to identify and address key knowledge gaps in plumbing, water, and mechanical systems, with the ultimate goal of advancing public health, environmental sustainability, and system efficiency.

The fund’s focus spans four core areas:

• Water and health: Supporting studies on biofilm behavior, microbial risks such as Legionella, and advancing water quality standards
• Innovative systems: Encouraging development of cutting-edge technologies and scalable green infrastructure
• Better tools: Including support for next-generation models that build on the success of the Water Demand Calculator
• Affordability and access: Investigating solutions that improve infrastructure affordability, resilience, and safety in underserved or disadvantaged communities

What makes the Innovation and Research Fund truly distinctive is its cross-sectoral approach. Traditional research efforts often occur in silos, limiting their practical impact. In contrast, IAPMO’s model intentionally bridges academia, industry, government, utilities, and nonprofit organizations — creating an ecosystem where research outcomes are both scientifically robust and implementation-ready.

In fact, one of the fund’s greatest strengths is its translational design. Rather than isolating research in academic journals, the Innovation and Research Fund prioritizes projects that can be rapidly integrated into real-world applications. This means insights gained don’t just sit on a shelf — they make their way into the built environment, benefiting engineers, installers, and end users alike.

This alignment between research and practical implementation is especially valuable in areas like tool development. For example, the Water Demand Calculator began as a theoretical model but evolved into a transformative sizing tool because its underlying data and assumptions were tested, refined, and validated through a collaborative and well-supported process. The Innovation and Research Fund aims to replicate this model of success across many other pressing challenges in the plumbing and water sectors.

For those interested in contributing to or benefiting from these efforts, IAPMO has created a centralized resource through its Support Innovation portal. The portal outlines current funding priorities, project categories, and submission guidelines, inviting partners from all backgrounds to join in shaping the future of water system design.

With the Innovation and Research Fund, IAPMO isn’t just investing in research — it’s investing in a smarter, safer, and more equitable future for our water systems.

Integration of ESPRI: Expanding research expertise

In May, IAPMO announced a significant advancement in its commitment to applied plumbing science: the integration of the Environmental Science, Policy and Research Institute (ESPRI) into its organizational structure. Led by Dr. Tim Bartrand, ESPRI has established itself as a leader in building water safety, disaster recovery, plumbing material research, and Legionella risk management.

ESPRI’s expertise encompasses a broad range of critical issues, including:

• Legionella risk assessment and mitigation
• Plumbing material evaluations and water chemistry interactions
• Disaster recovery guidance for plumbing systems after wildfires, floods, and contamination events
• Multi-family and institutional water management practices

By bringing ESPRI in-house, IAPMO has strengthened its scientific capabilities and broadened the scope of research questions it can credibly pursue. This integration enhances IAPMO’s ability to respond rapidly to emerging threats and collaborate across disciplines — from microbiology and public health to civil engineering and building design.

With ESPRI on board, IAPMO can now more fully support a whole-of-system approach to plumbing research, which accounts for:

• Biological, chemical, and physical interactions in water systems
• The real-life behavior of occupants and maintenance personnel
• Code implications, enforcement challenges, and practical solutions

This expanded capacity positions IAPMO uniquely to translate science into standards, ensuring that new knowledge informs the next generation of plumbing codes, products, and policies.

Summary and implications: A new era of plumbing research

For most of its history, the plumbing industry has operated on a static set of assumptions — standardized codes, tried-and-true sizing methodologies, and incremental design refinements. Yet in recent years, those foundational elements have begun to show their age. Outdated models like Hunter’s Curve, climate-driven resource stresses, and rising concerns over microbial water safety have exposed a critical truth: plumbing engineering cannot afford to remain reactive. It must become predictive. It must become scientific. And it must become strategic.

That recognition lies at the heart of IAPMO’s growing research ecosystem — a transformational blueprint anchored by three pillars: the Water Demand Calculator, the Innovation and Research Fund, and the integration of ESPRI. Each element represents a shift toward a future where data, collaboration, and public health shape how we design, build, and manage plumbing systems.

Plumbing research has lagged – until now

Historically, plumbing research has trailed behind other engineering disciplines. While transportation and structural design evolved through simulation, sensors, and feedback loops, plumbing often relied on intuition and legacy codes. This lag isn’t just academic — it has real consequences. Oversized systems drive up installation and energy costs, stagnant pipes increase pathogen risks, and inconsistent quality standards can jeopardize public trust.

The plumbing industry has long needed a credible, coordinated body to lead applied research. With its expansion into scientific development and collaboration, IAPMO is now answering that call.

A blueprint for research-driven change

The Water Demand Calculator initiated this shift. By replacing outdated assumptions with real fixture usage data, this tool helped right-size piping systems, reduce energy waste, and improve safety — all while saving on costs. It proved that better data means better design.

But the calculator was only the first step.

Recognizing that innovation requires investment, IAPMO launched the Innovation and Research Fund in April 2024. This cross-sector initiative supports projects in water quality, equitable infrastructure, green technology, and new sizing models. Unlike traditional academic grants, the fund emphasizes applied, translational work — science that moves from the lab into products, policies, and codes.

Then, in May, the integration of ESPRI marked the third major milestone. With its expertise in Legionella risk mitigation, disaster recovery, and plumbing materials science, ESPRI adds scientific firepower and field experience to IAPMO’s growing research engine. Together, these initiatives reflect a strategic redefinition of what a code body can be — not just a rules-maker, but a research leader.

Water will remain one of the defining challenges of this century. Urbanization, climate disruption, contamination events, and growing infrastructure inequities will demand bold thinking. But bold thinking requires partners.

Why this matters for everyone

The implications of this transformation extend beyond plumbing professionals. Consider the broader benefits:

• Engineers and designers now have tools that reflect real-world conditions, not just assumptions from 80 years ago.
• Contractors and builders gain efficiencies through optimized designs that reduce material and labor.
• Public health officials benefit from research that addresses emerging threats like Legionella and post-disaster contamination.
• Communities see tangible improvements in water access, safety, and sustainability.
• Researchers find a collaborative platform to test, scale, and apply their findings in impactful ways.

In essence, this is not just plumbing innovation — it’s infrastructure innovation, with water as the focal point.

A call to action: the road ahead

Water will remain one of the defining challenges of this century. Urbanization, climate disruption, contamination events and growing infrastructure inequities will demand bold thinking. But bold thinking requires partners.

That’s why IAPMO is calling on utilities, public health agencies, universities, manufacturers, and fellow engineers to get involved. Whether you have data to share, technologies to test, or a problem you want to solve, there is a place for you in this ecosystem.

Here’s how you can engage:

• Explore the Water Demand Calculator
  Get familiar with the tool that’s changing how we size water systems: iapmo.org/water-demand-calculator
• Support Innovation
  Help fund or propose high-impact studies through IAPMO’s Innovation and Research Fund: iapmo.org/research/support-innovation
• Learn About ESPRI Integration
  Read how this nationally recognized research institute is enhancing plumbing safety: ESPRI addition announcement
• Stay Updated on the Research Fund
  Track new opportunities, research priorities, and grant cycles: Innovation Research Fund announcement

Join the movement

What IAPMO has created is more than a suite of tools — it’s a call for cultural change in plumbing science, one that values precision over guesswork, integration over silos, and science over the status quo.

If you’re a plumbing engineer seeking smarter tools, a policymaker focused on resilience, or a funder looking for high-impact infrastructure innovation, the moment is now. Because in a world of growing water complexity, waiting for the future is no longer an option.

We must build it — together.