Sabine Postma, Gretchen Richter, Bea Covington, Gretchen Greene
On-site sewage systems (OSS) serve as critical wastewater treatment infrastructure for hundreds of thousands of households across the Puget Sound region. However, aging systems present mounting challenges for public health, environmental protection, and household financial stability. This study examines the economic burden borne by homeowners to address failing OSS through comprehensive case studies in King County and across twelve Puget Sound counties.Using data from Public Health—Seattle & King County, Washington Department of Health, and Craft3, we estimate that King County homeowners face a collective $3.7 billion burden to address OSS older than 20 years, with nearly $3 billion needed immediately for systems exceeding their 30-year lifespan. Regionally, assuming a 3% annual failure rate, repair and replacement costs approach $500 million annually, with $77.5 million attributed to systems within Marine Recovery Areas that directly impact water quality.Location and infrastructure availability create significant cost disparities, with homeowner expenses ranging from $4,000 for basic OSS maintenance to $124,000 for sewer connections. These findings underscore the “wicked” nature of OSS management, where individual property owners bear responsibility for infrastructure providing significant public benefits. We also examine innovative financing mechanisms, including green bonds, community-based partnerships, and Chile’s Subdirectorate of Rural Health Services, offering potential pathways for addressing this critical infrastructure challenge.