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.

Why is PWSA turning to orthophosphate now?

PWSA currently uses soda ash for corrosion control. This wasn’t always the case.

After a year-long study, PWSA said it determined orthophosphate would be more effective than soda ash and the DEP agreed. In May, the DEP approved PWSA’s corrosion control upgrade to orthophosphate.

PWSA has said it hopes orthophosphate will reduce lead levels more quickly while the authority continues replacing lead service lines across the city, estimating that about 12,500 of some 71,000 residential service connections contain lead.

The EPA says lead concentrations in drinking water should be below the EPA’s own action level of 15 parts per billion, but advocates say that threshold is set way too high. In July, PWSA testing found lead levels at 10 ppb — the lowest level in eight years.

According to the CDC, no safe blood lead level in children has been identified.

When is it happening?

Lauren Fraley, community relations coordinator with the DEP, told The Incline that the department “has not issued a construction permit for the use of orthophosphate but expects to make a decision on PWSA’s application in the near future.”

In anticipation of that, PWSA said its crews have already begun extended water main flushing across the service area to prepare the system for the addition of orthophosphate.

Will it work?

Dzombak said orthophosphate has proven effective as a corrosion control elsewhere.

PWSA said hundreds of water suppliers across the country have adopted orthophosphate in their treatment processes.

“Many water utilities have been safely using phosphates since the passage of the Environmental Protection Agency’s (EPA) Lead and Copper Rule (1992) to reduce lead and copper levels in tap water,” the Washington Suburban Sanitary Commission’s website notes.

Leonard Casson, a civil and environmental engineering researcher with Pitt’s Swanson School of Engineering, said, “Of all the options out there now, I wouldn’t say orthophosphate is the panacea of all corrosion control methodologies, but it’s something that has been implemented elsewhere and successfully used to make sure you’re getting a film on the inside of the pipe and that lead is significantly reduced.”

How much orthophosphate is PWSA planning to use?

PWSA says a level of orthophosphate of 3.5 milligrams/liter will be applied through the first six months to expedite the lead corrosion control.

“As the coating adheres to the pipes and we observe the lowering of lead levels, we’ll switch to a maintenance level of 1 milligram/liter,” PWSA spokesperson Rebecca Zito said.

“We will monitor the application and resultant levels of orthophosphate to confirm that levels are acceptable throughout the system.”

Zito said concentrations of orthophosphate will be minimal when water reaches someone’s house.

“Initially it will be less than 3.5 milligrams/liter. When the application rate is lowered to the maintenance level, orthophosphate levels will be less than 1 milligram/liter.”

Casson said this “sounds like a reasonable approach to the corrosion control issue using a standard operating procedure.”

Dzombak added: “The dosing range that you cite (1.0-3.5 mg/L) is a typical dosing range for orthophosphate addition to drinking water systems for corrosion control. The effective dose depends on the particular water chemistry. PWSA will monitor the effectiveness of the dose, and adjust accordingly. Adding the chemical costs money. PWSA has every incentive to keep the dose at the minimum that is effective.”

Are there consumption risks?

The EPA says “The health effects of drinking water with phosphates are not known,” while the FDA considers phosphates as a food additive to be “generally recognized as safe.”

PWSA said via email that orthophosphate is both an effective anti-corrosion measure and safe to consume.

Some research suggests a connection between excessive levels of phosphate consumption and cardiovascular problems or complications from renal disease. High concentrations of phosphoric acid, a source of orthophosphate, in soft drinks have been linked to tooth enamel loss and kidney problems, as well.

But the EPA says the typical phosphate levels found in a liter of drinking water are about 100 times lower then the phosphate levels found in the average American diet. “For example, a person would have to drink ten to fifteen liters of water to equal the amount of phosphates in just one can of soda,” the agency reports.

What about the environment?

Maybe the most controversial aspect of orthophosphate as a water treatment measure involves its potential for adverse environmental impacts, according to a study by Lancaster University and the British Geological Survey (BGS).

In high concentrations, orthophosphate, an ingredient in fertilizers, can cause rapid algae growth in surface waters, which can deplete sunlight and oxygen levels and harm fish populations, the study found. This is a process known as eutrophication, defined as the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen, phosphorus, or both.

In an email, DEP said it’s aware that nutrients such as phosphate and orthophosphate can cause eutrophication in waterways, adding, “However, under normal conditions, treated drinking water wouldn’t be discharged directly into waterways.”

PWSA water is treated post-consumer at the Alcosan facility, where federal pollution discharge standards apply.

But some water will inevitably escape the system before it gets there, most likely during heavy rain storms that cause sewer system overflows “when the system is overwhelmed,” Zito said.

In such a scenario, Dzombak said orthophosphate concentrations would at least be diluted before reaching natural bodies of water.

Dzombak said orthophosphate releases from agricultural sources are typically much larger ecological threats than those from municipal water systems both due to volume and concentration levels.

What happened in other cities?

Casson said orthophosphate “helped solve” DC’s lead water problem and that it’s helped manage lead levels in drinking water in other cities. He points to its widespread adoption by water systems worldwide in making the case that it’s considered both effective and safe.

It’s not without some side effects, however.

When bacteria levels in D.C. tap water spiked in 2004, exceeding federal standards for the first time since 1996, officials surmised that the addition of orthophosphate to the system may have “shaken off a layer of rust and bacteria inside city water pipes,” the Washington Post reported at the time.

In Flint, increased levels of phosphates and pH were linked to a white residue that began to appear in pots and pans after water was boiled. Officials called the reaction “harmless and perfectly normal” and vowed to continue monitoring it.

According to a 2002 peer-reviewed article in the Journal AWWA, many utilities “are aware of potential drawbacks of inhibitors [like orthophosphate], especially increased biological activity [like eutrophication] and more treatment costs and residuals.”

PWSA’s research included reaching out to water officials in cities where orthophosphate has been successfully adopted as a treatment component, Zito said.

“It has successfully been used by DC Water and Cleveland Water. It is presently used by Pennsylvania American’s water supplied to Pittsburgh’s South Hills customers, among 100’s of other United States water suppliers,” she said.

Does this move make sense?

Casson said it does, given PWSA is currently “behind the eight ball” in combating the city’s lead water crisis. And while he can’t categorically say that orthophosphate is safe, he said lead exposure presents a very clear and present danger.

“This is a reasonable course of action to manage lead levels until they can figure out the replacement of lead service lines. […] Of the options available from a public health perspective, it is better they do something, even if it’s just for a period of time, than to do nothing and expose the public and drinking water to higher concentrations of lead.”

Casson added, “Would it be great if all lead lines were replaced and we never had to worry about lead again? Yes, that would be fantastic. But using orthophosphate is a practical solution and it’s better to do something to protect the public than do nothing.”