U.S. Plumbing Codes Size Pipes Using 1940s Data, Causing the Water Safety Problems They're Supposed to Prevent

Plumbing designers in the United States size building water pipes using "Hunter's Curve," a demand model developed in 1940. Modern fixtures use a fraction of the water that 1940s fixtures did, but the design standard was never updated. The result is systematically oversized pipes that increase water residence time, directly promoting bacterial growth (including Legionella) and chemical leaching (including lead). Buildings that comply with current plumbing codes are, paradoxically, less safe than buildings with properly sized pipes — the regulation itself creates the hazard.

NIST identified nearly 60 specific research needs stemming from this measurement gap. Oversized pipes create stagnant water zones where Legionella proliferates — Legionnaires' disease kills approximately 1,000 Americans annually and hospitalizes 10,000+. Lead contamination in drinking water persists partly because codes produce pipe configurations that maximize contact time between water and plumbing materials. 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and residential buildings constructed annually in the U.S. are all designed to a demand model that is 85+ years out of date.

NIST, EPA WaterSense, and the Water Research Foundation organized a Measurement Science Roadmap Workshop in August 2018, producing a comprehensive gap analysis (GCR 19-020). NIST TN 2088 distilled this into prioritized research needs. 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 this data requires metering at the fixture level, which is expensive and invasive. Plumbing codes are set by model code organizations (IAPMO, ICC) that update on multi-year cycles and require political consensus. Plumbing is regulated at the local level with strong jurisdictional authority — federal research recommendations have no binding force. The research community has identified what needs to happen but converting findings into "actionable research programs" with "timelines, commitments by stakeholder organizations, and specific deliverables" has not occurred.

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 monitoring (where smart meters have driven similar design standard updates) provides a methodological template.

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. Relevant disciplines: civil/environmental engineering, plumbing/mechanical systems, data science, public health.