As part of the Pittsburgh Water and Sewer Authority’s Community Lead Response, we are beginning to use orthophosphate to reduce lead levels in tap water. Orthophosphate is a food-grade additive that demonstrated to be very effective at reducing corrosions from lead pipes.

A year-long study found orthophosphate to be more effective at reducing corrosion than our previous treatment method using soda ash and lime. The Pennsylvania Department of Environmental Protection (PA DEP) agreed with the study’s findings and approved corrosion control upgrade to orthophosphate.

Water systems in large cities across the country use orthophosphate successfully to reduce the risk of lead in water, including sections of the City of Pittsburgh served by Pennsylvania American Water Company.

We have built four new facilities to add orthophosphate to the water distribution system. Beginning in spring 2019, we are flushing the distribution system by opening hydrants in preparation to add the orthophosphate.

Frequently Asked Questions

Orthophosphate is a food-grade additive that we will begin adding out our treatment plants to help reduce lead levels in water. When water with orthophosphate runs through the system, it will create a coating on the inside of lead service lines, creating a barrier between the lead pipes and the water. This is called “corrosion control”. PWSA currently uses soda ash and lime for corrosion control but has found that orthophosphate will work even better.

The Environmental Protection Agency (EPA) and the Pennsylvania Department of Environmental Protection (PA DEP) recognizes orthophosphate as an effective additive in water in reducing lead levels. It is also recognized as safe by the U.S. Food and Drug Administration.

PWSA conducted a year-long study of several different additives that are used to reduce lead levels in water. After finding that orthophosphate would be most effective for PWSA’s system, the research was reviewed extensively by the PA DEP before being approved as part of the treatment process. Orthophosphate is used for corrosion control in Boston, Washington, DC, Cleveland, and Philadelphia. It is also used by Pennsylvania American Water Company who serve some customers in the City of Pittsburgh.

PWSA exceeded the action level for drinking water in June 2016. Since then, we have been working to aggressively replace lead service lines. However, replacing every lead service line will take years. In the immediate term, an effective solution to address high lead levels is to use the most effective corrosion control, which benefits our entire drinking water system.

Before PWSA can begin to add orthophosphate-treated water into the system, it must flush the water distribution system. To do this, PWSA crews will be strategically traveling through the drinking water system opening hydrants to let the water flush out of the mains in the street. This will help the water with orthophosphate create the protective barrier necessary for corrosion control.

Crews have started flushing our largest water mains in the system, working 24/7.

Over the next few months, customers may see crews opening hydrants and performing water quality monitoring. Customers located near flushing areas may notice temporary brown or discolored water. To clear discolored water, customers can use the following instructions:


  1. Run cold taps at the lowest point in the building for about 10 minutes or until the water runs clear.
  2. If it is still not clear, wait about 30 minutes and try flushing with cold water again.
  3. If the issue persists, contact PWSA Customer Service at 412-255-2423 and a representative can assist in addressing the issue at your property.


PWSA’s Water Quality team will perform ongoing water quality monitoring and analyze hundreds of water samples during the implementation of orthophosphate. The Authority is working closely with the Pennsylvania Department of Environmental Protection (DEP) to ensure the transition to orthophosphate goes smoothly.

To read more, go to PWSA’s March press release on orthophosphate and hydrant flushing.

For any questions or concerns about hydrant flushing while we prepare for orthophosphate, contact PWSA Customer Service at 412-255-2423.