10 things you need to know about orthophosphate, coming soon to Pittsburgh drinking water

Is it safe? Is it environmentally friendly? Will it work?


In an effort to further reduce lead levels in city drinking water, the Pittsburgh Water and Sewer Authority is preparing to add a new chemical to the supply here aimed at forming a natural, protective barrier between lead pipes and the water we consume.

That additive is orthophosphate, already in use as a lead control measure in New York City, Philadelphia, Washington, D.C., Flint, Mich., and elsewhere. PWSA says orthophosphate could reduce lead levels in a matter of months.

But how does it work? Is it safe? Is it environmentally friendly? And what do the experts think of the authority’s plan?

To answer those questions and more, we spoke with the DEP, PWSA, and local water management experts, and we consulted published research on the subject. Here’s what we found.

What is orthophosphate?

Orthophosphate is a member of the phosphate family. Phosphates are naturally occurring and mined in states like Florida and North Carolina.

Forms like orthophosphate are often used in agricultural fertilizers. They’re also added to processed foods and naturally present in many foods, albeit at much lower levels, the USDA explains. The simplest source of orthophosphate is phosphoric acid, per the Environmental Protection Agency.

Increasingly, orthophosphate is added to water systems to delay corrosion of metal pipes and prevent heavy metals like lead from leaching into the water. Often it’s added as phosphoric acid, a colorless and tasteless chemical, according to the Washington Post.

How does it work?

Lead is usually introduced to drinking water by corroded lead pipes. When water sits in those pipes, lead can leach into the water supply and accumulate to dangerous levels, per the Centers for Disease Control and Prevention.

Orthophosphate “has an affinity for the surfaces of metal pipes” and clings there, said Dave Dzombak, department head and professor of Civil and Environmental Engineering at Carnegie Mellon University.

That forms a protective coating inside water pipes that helps reduce corrosion and the leaching that can result in lead being transferred into the water supply.

Phosphates also attract and sequester minerals like calcium which help form a “protective coating of insoluble mineral scale on the inside of service lines and household plumbing,” according to the EPA.