water · infrastructure · family: the regulator demands evidence that cannot exist
pipes sized bya 1940s formula
U.S. Plumbing codes size pipes using 1940s data, causing the water safety problems they're supposed to prevent
Problem statement
Plumbing designers in the United States size building water pipes using "Hunter's Curve," a demand model developed in 1940. Modern low-flow fixtures use less water than the fixtures Hunter's data were based on, and the model is still in use; NIST notes that IAPMO and ASPE developed a Water Demand Calculator for single- and multi-family dwellings, incorporated into the IAPMO Uniform Plumbing Code (IAPMO, 2018), but lists water use data to replace Hunter's Curves as an open research need. The result, NIST says, is that the method tends to oversize water supply piping, particularly when low-flow fixtures are used; oversized pipes mean lower flows and longer water residence time, which give bacteria more time to grow (Legionella is among the pathogens the report discusses) and give plumbing materials more opportunity to dissolve into the water. Buildings that comply with current plumbing codes can therefore carry a water-quality risk, because, as NIST puts it, those codes "do not fully account for increased water efficiency in fixtures and appliances."
Why this matters
NIST identified nearly 60 specific research needs stemming from this measurement gap. Oversized pipes create low-flow and stagnant conditions that, in NIST's words, "provide more time for bacteria to grow inside plumbing systems and for the breakdown of disinfectant residual levels." Longer residence time also gives more opportunity for reactions between water and piping materials, and lead is among the contaminants NIST says should be monitored at the point of use. Hunter's Curve, introduced in 1940, is in NIST's words "still used today" and "still provides a design demand value" in current plumbing codes.
What’s been tried and why it hasn’t worked
NIST, EPA WaterSense, and the Water Research Foundation organized a Measurement Science Roadmap Workshop in August 2018, producing a workshop synthesis (GCR 19-020). NIST TN 2088 combined the workshop's priorities with responses to a Federal Register notice and stakeholder discussions into a list of research needs, and says work is still needed to prioritize them. However, there is no national, accessible, consistently compiled database of how water is actually used in different building types — the foundational data needed to replace Hunter's Curve. Collecting these data requires better and less expensive meters; NIST lists reducing meter installation and operation costs as a research need in its own right. Plumbing codes are set by two major model code organizations (IAPMO, ICC), no single plumbing code is universally recognized, and local jurisdictions lag in adopting the latest model codes and vary in how they adopt, modify and enforce them. The research community has identified what needs to happen, but NIST TN 2088 says "significant efforts are needed" to convert these needs into "actionable research programs," starting with an implementation plan and roadmap that "would include timelines for specific programs and projects, commitments by stakeholder organizations to take the lead on various elements, and specific deliverables expected from each effort."
What would unlock progress
A modern, validated water demand model based on actual fixture-level usage data from contemporary buildings — essentially "Hunter's Curve 2.0." This requires distributed low-cost water metering technology deployed across a representative sample of building types and climates. Sensor miniaturization and IoT connectivity have made this technically feasible in ways it wasn't even a decade ago. The adjacent field of building energy analysis, which NIST cites as the model for developing reference buildings, may provide a methodological template.
Entry points for student teams
A team could instrument a campus building with fixture-level flow meters, collect usage data over a semester, compare measured demand to Hunter's Curve predictions, and quantify the oversizing factor. This is achievable with off-the-shelf IoT flow sensors and a microcontroller data logger. The result would be a direct, publishable contribution to the measurement gap NIST identified. A team without building access could instead take a set of published residential building plans, size the supply piping both by Hunter's Curve and by the IAPMO/ASPE Water Demand Calculator that NIST describes, and report how far the two methods diverge and where the difference in pipe volume would fall. Relevant disciplines: civil/environmental engineering, plumbing/mechanical systems, data science, public health.
Genes
Structural cousins: stuck the same way, in other fields
Sources
NIST TN 2088, "Measurement Science Research Needs for Premise Plumbing Systems," NIST, 2020; NIST GCR 19-020, "Measurement Science Roadmap Workshop for Water Use Efficiency and Water Quality in Premise Plumbing Systems: August 1-2, 2018," NIST, December 2018. ; go to source 1 ↗ go to source 2 ↗
Working notes
Notes made while writing and checking this brief, shown as written. They use working shorthand.
- NIST TN 2088 identifies nearly 60 research needs; the Hunter's Curve issue is the most structurally dramatic because the codes' own sizing method tends to oversize the pipes.
- Related to existing briefs on water infrastructure (`water-aging-pipe-network-failure-prediction`) but this is about design codes for new buildings, not detection in aging ones.
- The Legionella connection makes this a safety-critical regulatory mismatch, not merely an efficiency issue.
- EPA WaterSense program is a potential partner for any student research in this space.
- Plumbing code organizations (IAPMO, ICC) would be interested in real-world demand data that could inform code revisions.
Reconciliation 2026-09-30: Both sources were read in full on 2026-09-30: NIST TN 2088 (79 pages, fetched from https://nvlpubs.nist.gov/nistpubs/TechnicalNotes/NIST.TN.2088.pdf) and NIST GCR 19-020 (44 pages, fetched from https://nvlpubs.nist.gov/nistpubs/gcr/2019/NIST.GCR.19-020.pdf). (1) The Source line gave GCR 19-020 as "NIST, 2019" with a shortened title; the document's cover reads "Measurement Science Roadmap Workshop for Water Use Efficiency and Water Quality in Premise Plumbing Systems: August 1-2, 2018," dated December 2018, and TN 2088 cites it as Pickering et al. 2018. The Source line now carries the cover title and date, and the report's own DOI link. (2) "The design standard was never updated" was contradicted: TN 2088 describes a Water Demand Calculator developed by IAPMO and ASPE for single- and multi-family dwellings and incorporated into the IAPMO Uniform Plumbing Code (IAPMO, 2018), while still listing water use data to replace Hunter's Curves as a research need. The sentence now says both. (3) "Modern fixtures use a fraction of the water that 1940s fixtures did" is not in the sources; TN 2088 gives a 22 % drop in indoor use for a typical single-family home over two decades and says the method oversizes "particularly when low-flow fixtures are used." The text now says low-flow fixtures use less water than the fixtures Hunter's data were based on. (4) "Systematically oversized pipes ... directly promoting bacterial growth ... and chemical leaching," and "the regulation itself creates the hazard," were stronger than the source, which says the results "tend to oversize" piping, that low flow or stagnant conditions "provide more time for bacteria to grow," that longer residence gives "more opportunity for materials to dissolve into the water," and that plumbing system design "may be a contributing factor," and that codes "do not fully account for increased water efficiency in fixtures and appliances." The sentences now follow that wording. (5) "Legionnaires' disease kills approximately 1,000 Americans annually and hospitalizes 10,000+" is in neither source and was removed. (6) "The 400,000+ commercial and residential buildings constructed annually in the U.S. are all designed to a demand model that is 85+ years out of date" is in neither source; the building count and the age were removed, and the sentence now quotes TN 2088: Hunter's Curve is "still used today" and "still provides a design demand value." (7) "Lead contamination ... persists partly because codes produce pipe configurations that maximize contact time" is not in the sources; the text now says longer residence time gives more opportunity for reactions with piping materials and that lead is among the contaminants NIST says to monitor at the point of use. (8) GCR 19-020 was called "a comprehensive gap analysis"; its cover calls it a workshop synthesis, and the text now says so. (9) "NIST TN 2088 distilled this into prioritized research needs" was contradicted: TN 2088 says its needs came from the workshop priorities, a Federal Register notice and stakeholder discussions, and that "work is still needed to prioritize these needs." The sentence now says that. (10) "Metering at the fixture level, which is expensive and invasive" is not in the sources; TN 2088 lists "improved and less expensive meters" as a research need and says installation and operation costs need to be reduced. The text now says that. (11) That IAPMO and ICC "update on multi-year cycles and require political consensus," and that "federal research recommendations have no binding force," are not in the sources; TN 2088 says IAPMO and ICC are the two major model code development organizations, that no single plumbing code is universally recognized, and that local jurisdictions lag in adoption and vary in how codes are adopted, modified and enforced. The text now follows that. (12) The quoted phrase "timelines, commitments by stakeholder organizations, and specific deliverables" was a condensation presented as a quotation, and "has not occurred" is not in the source; the text now quotes TN 2088's own words ("significant efforts are needed," and the full sentence on timelines, commitments and deliverables) as a plan the report calls for. (13) That smart meters "have driven similar design standard updates" in building energy is not in the sources; TN 2088 cites building energy analysis as the model for reference buildings, and the sentence now says that. (14) In the Source Notes, "because the regulation actively causes harm" was softened to the source's claim that the sizing method tends to oversize the pipes. (15) A second entry point that needs no building access was added, built on the IAPMO/ASPE Water Demand Calculator TN 2088 describes, scoped to residential plans because the source says the calculator covers single- and multi-family dwellings. Confirmed in the sources and left as written: Hunter's Curve introduced in 1940 by Roy Hunter at the National Bureau of Standards and still used today; the count of research needs (59 topics listed across Tables ES-1 and ES-2, so "nearly 60" stands, although the report does not state a total); the August 2018 workshop organized by NIST, EPA and the Water Research Foundation and prepared for EPA WaterSense; the need for "national, accessible, and consistently compiled" water use databases (GCR 19-020); the quoted phrase "actionable research programs"; the TN 2088 title and 2020 date. Not changed but noted for the editor: the long title's "Causing the Water Safety Problems" is stronger than the sources' "potential negative consequences" and "may be a contributing factor"; no number in either title was wrong, so the titles were left as they were. Genome Tags untouched. A second reader went over these repairs on the same day against both sources, read in full, and tightened four sentences to the sources' own wording (the Uniform Plumbing Code citation, the closing sentence of the Problem Statement, the "still used today" sentence, and the residential scope of the second entry point); every repair otherwise stands.