University of Pittsburgh researchers have unveiled startling evidence about the unintended consequences of a widely used drinking water treatment practice on urban waterways. Their recent study, published in PLOS Water, shines a light on the environmental ripple effects caused by the addition of orthophosphate to municipal water supplies. Orthophosphate is added to reduce the corrosion of aging lead pipes, a critical public health measure designed to limit the release of toxic lead into drinking water. However, this intervention is altering the chemistry of nearby urban streams, raising concerns about nutrient pollution and aquatic ecosystem health.
The use of orthophosphate corrosion inhibitors in drinking water systems has long been recognized as an effective solution to prevent lead leaching from deteriorating infrastructure. Yet, the new findings highlight that these phosphate compounds are not contained within the distribution network as previously assumed, but instead leak into surrounding environments through this aging infrastructure. This leakage significantly elevates phosphorus levels in urban streams, a nutrient commonly linked to eutrophication—a process that triggers excessive algal and plant growth, resulting in oxygen depletion and the decline of aquatic life.
Focusing their investigation on five urban streams in Pittsburgh, the researchers conducted an extensive analysis of stream water chemistry before, during, and after orthophosphate dosing was implemented between 2019 and 2020. The data revealed a dramatic elevation in phosphorus concentrations in these streams, with levels surging by more than 600%. This startling increase correlates with a parallel rise in trace metals such as copper, iron, and manganese by nearly 3,500%, indicative of the co-transport of corrosion byproducts alongside the phosphate additives.
“The magnitude and clarity of changes in urban stream chemistry were unexpected,” stated Dr. Anusha Balangoda, the study’s lead author and Assistant Teaching Professor at the University of Pittsburgh. Her remarks underscore the revelation that subsurface water infrastructure cannot be considered an isolated system. Instead, it acts as a conduit influencing adjacent ecosystems, defying prior assumptions about the impermeability of underground pipes and their containment of additives.
Co-author Dr. Emily Elliott, who chairs the Pittsburgh Water Collaboratory, calls attention to the delicate balance needed between public health protections and environmental stewardship. “While safeguarding populations from lead exposure remains paramount, our work reveals an urgent need to concurrently consider the downstream ecological consequences of water treatment methods,” she explained. This dual challenge necessitates a nuanced approach to managing water systems that protect human health without compromising freshwater ecosystems.
The backdrop to this study involves a troubling history of lead contamination crises, from Flint, Michigan to Washington, D.C., and here in Pittsburgh. These public health emergencies have precipitated widespread adoption of phosphate-based corrosion inhibitors, but while their efficacy in reducing lead exposure is documented, their environmental footprint has received limited investigation. This research fills a critical knowledge gap by identifying the pathway through which phosphate escapes pipes—not from conventional pollution sources like wastewater or industry, but via leaks in aging drinking water infrastructure.
Sampling methods included monthly water chemistry assessments and nutrient addition bioassays, whereby researchers introduced controlled phosphorus levels and observed algal growth responses. These meticulous protocols confirmed the ecological threat orthophosphate poses once it departs the distribution system, intensifying nutrient loading that can drive harmful algal blooms and deteriorate water quality in urban streams.
The implications stretch well beyond Pittsburgh. With millions of Americans inhabiting regions across the Northeast, Great Lakes, and Midwest serviced by similar lead pipe networks and orthophosphate dosing programs, this phenomenon is potentially widespread. The study amplifies the call for a nationwide reevaluation of how aging infrastructure management intersects with ecological health, advocating for comprehensive frameworks to safeguard both human and environmental well-being.
To address these challenges, the researchers urge swift action focusing on the urgent repair and modernization of deteriorating pipe networks, noting that current systems lose 40-50% of treated water through leaks and main breaks. Such infrastructural decay not only wastes valuable water resources but also becomes a vector for nutrient enrichment of groundwater and surface streams, exacerbating pollution problems.
Enhancing wastewater treatment represents a complementary strategy. Many treatment plants currently lack advanced tertiary phosphorus removal technologies capable of reducing effluent phosphorus loads by 80-99%. Implementing these processes is critical, especially since the study observed a 26% increase in phosphorus discharge from these facilities correlated with orthophosphate treatment implementation.
Adjustment of orthophosphate dosing concentrations to optimize the minimum effective level for corrosion control is another key recommendation. Refining treatment strategies to balance human health imperatives with environmental safeguards could significantly mitigate ecological damage without compromising lead exposure prevention.
Finally, the authors emphasize the importance of developing innovative monitoring and analytical tools to better understand and manage the complex interactions between drinking water infrastructure and downstream ecosystems. Improving real-time assessments of subsurface leakages and additive transport will inform adaptive management approaches and policy decisions.
Dr. Elliott encapsulated the broad significance of these findings: “Our study reveals that the challenges posed by aging lead pipes and orthophosphate treatment are not isolated. They are part of a widespread national issue requiring coordinated action spanning infrastructure repair, environmental monitoring, and public policy.” Such integrated solutions are essential for securing safe drinking water while protecting the vitality of urban aquatic ecosystems.
This groundbreaking research was supported by the National Science Foundation RAPID funding program and the Pittsburgh Water Collaboratory, with instrumental cooperation from the Pittsburgh Water and Sewer Authority providing critical sampling and water treatment data. Their collaboration underscores the power of interdisciplinary partnerships in unveiling hidden environmental issues linked to urban water systems.
As cities continue grappling with legacy infrastructure and evolving water quality mandates, this study serves as a clarion call. Ensuring water safety involves more than just removing contaminants; it demands a holistic appreciation of how treatment techniques ripple through our interconnected water environments. The findings open a vital dialogue about sustainable water management strategies capable of preserving public health alongside the integrity of freshwater ecosystems in urban landscapes nationwide.
Subject of Research: Not applicable
Article Title: From Pipes to Streams: The Hidden Influence of Orthophosphate Additions on Urban Waterways
News Publication Date: 13-Nov-2025
Image Credits: Credit: PLOS Water, et. al.
Keywords: Earth sciences, Water management
