DC’s Main Sewer Overwhelmed by Immigration-Driven Growth

As the population of the DC metro area expanded, rising wastewater loads steadily rendered the sewer system less resilient to sustained high flows.

The Spill

The largest sewage spill in U.S. history started on January 19, 2026, when a section of the region’s largest wastewater pipeline — the Potomac Interceptor — collapsed. For eight straight days, a torrent of raw sewage discharged into the Potomac River, with a total waste volume of about 240 million gallons. The event caused significant ecological harm to the river, with impacts that will persist for years.

Built for Fewer People

The Interceptor served some of the region’s densest and oldest communities, including portions of Washington, D.C. and adjacent urban areas in Fairfax and Montgomery counties. Since the pipe’s construction in 1962, the population of its service area has grown by several million people. In several recent years, international migration accounted for a large majority of population gains in the Washington, D.C. metro area, in some cases exceeding 70%. More specifically, in 2015, roughly 21% of the metro population was foreign-born, compared to about 25% — approximately 1.6 million — today.

Growth Burden

From an infrastructure perspective, total wastewater load rises as population increases. The duration of high-flow stress, peak flows during wet weather, and cumulative fatigue on aging pipes all increase, reducing safety margins. As pipes approach — and sometimes exceed — their operating limits, sewer systems become more vulnerable to structural failures.

Out of Sight, Out of Mind

Policymakers would serve their citizenry well by employing a more balanced and sustainable perspective on immigration policy. Immigration-driven population growth is frequently celebrated for expanding the tax base and gross domestic product (GDP). But the corresponding costs for public services can be far less visible, especially for buried infrastructure like sewer lines.

A National Pattern

Washington’s experience is not unique. Many growing U.S. metro areas rely on sewer systems approaching obsolescence. Population growth increases sewage loads, while aging infrastructure becomes less resilient to sustained high flows. Budget tradeoffs, however, often delay replacement.

A Policy Gamble

By failing to account for limited infrastructure capacity, Washington’s policymakers gambled with destiny. Instead of prioritizing the replacement of outdated sewer pipes, capital investments were allocated to serve housing, transportation, and schools.

Why Slower Growth Matters

Growth rates directly affect resilience. Slower population growth does not eliminate the need for infrastructure upgrades, but it can buy time. Reducing immigration levels can help cities catch up on accumulated infrastructure deficits, restoring safety margins that were eroded by persistent population growth.

A More Sustainable Path

The nation’s network of capacity-constrained utilities and infrastructure–especially in dense metro areas like Washington–would benefit significantly from slower population growth; and the most practical means for achieving less growth is by reducing immigration levels. Doing so would give cities time and resources to inspect, rehabilitate, and replace aging systems to prevent calamitous failures in the future.