The Philadelphia Water Department (PWD) delivers water that consistently meets or exceeds all federal and state standards for drinking water safety set by the Environmental Protection Agency (EPA) and the Pennsylvania Department of Environmental Protection (PADEP). The water supply is considered safe when it leaves the treatment plants and throughout the public distribution system. However, contamination can occur within older, privately owned service lines connecting the public water main to individual homes. The PWD manages safety assurance through continuous monitoring and a multi-step purification process.
The Origin and Purification Process
Philadelphia’s water supply is drawn from two main sources: the Delaware River and the Schuylkill River, which contribute approximately half of the city’s total supply each. This dual-source system provides a measure of security and resilience for the regional water infrastructure. The water is processed at three major treatment plants: the Samuel S. Baxter plant on the Delaware River, and the Queen Lane and Belmont plants on the Schuylkill River.
The purification process begins with the raw river water undergoing natural settling in reservoirs or basins, allowing heavier sediments to fall out. The water then enters the coagulation phase, where specific chemicals are added to encourage smaller particles to clump together. This is followed by flocculation, a gentle mixing process that ensures the chemicals blend well with the particles, making them heavy enough to settle during the subsequent sedimentation phase.
The clarified water is then passed through filters made of materials like sand and gravel to remove any remaining fine particles. Disinfection is performed by adding chlorine to eliminate disease-causing pathogens, with ammonia added later to form chloramine, which helps maintain disinfection throughout the distribution system. Finally, zinc orthophosphate is added to coat the interior of pipes, acting as a corrosion inhibitor to minimize the leaching of metals like lead from plumbing materials.
Current Quality Assurance and Testing Standards
The safety of Philadelphia’s water post-treatment is maintained through a rigorous framework of testing and compliance with the federal Safe Drinking Water Act. The PWD monitors for approximately 100 regulated contaminants, including microbial, inorganic, and organic chemicals. Monitoring occurs at various stages, from the source rivers to the final delivery points.
To ensure water remains safe in the 3,100 miles of water mains, the PWD collects and tests samples throughout the distribution system multiple times daily. For instance, the residual chlorine level is checked over 400 times each month to confirm proper disinfection levels are maintained. The city also tests for emerging contaminants, such as Per- and Polyfluoroalkyl Substances (PFAS), in anticipation of future federal regulations.
The PWD publishes an Annual Water Quality Report, also known as a Consumer Confidence Report (CCR), which details the results of all required testing. This report confirms that the water meets or exceeds all mandated limits for regulated substances. Residents can access this report to review the specific data on contaminants and the city’s compliance record.
Understanding the Risk of Lead Service Lines
The primary concern for household water safety in Philadelphia is the presence of lead service lines, which are the pipes connecting the city’s water main to a private home’s internal plumbing. While the water leaving the treatment plants is lead-free, lead can leach into the water as it sits in these older lines, particularly in homes built before the 1950s. The PWD estimates that 20,000 to 25,000 homes may still have these service lines.
To mitigate this risk, residents with known or suspected lead service lines should take additional precautions, even though the PWD treats the water to reduce corrosion and lead release. One simple action is flushing the pipes by running the cold water tap for three to five minutes, especially after the water has been sitting unused for several hours, such as overnight.
The PWD is actively working to address this infrastructure challenge, offering programs like the Homeowners Emergency Loan Program (HELP), a zero-interest loan to cover replacement costs for the privately owned portion of the line. The city also received significant federal funding to accelerate the replacement of these lead lines. Residents can use a filter certified by an American National Standards Institute (ANSI) accredited certifier specifically for lead removal to further reduce exposure.