Corrosion Control

Cobb County-Marietta Water Authority (CCMWA) is dedicated to providing safe drinking water and has proactively transitioned to orthophosphate treatment to optimize corrosion control and address public concerns regarding pinhole leaks in premise plumbing. While our water system has historically maintained lead and copper levels well below Federal Action Levels, extensive scientific studies led to the implementation of this advanced treatment method to provide a higher level of protection for our customers' private plumbing.

Understanding the Investigation into Pinhole Leaks

For several years, CCMWA investigated reports of copper pitting and pinhole leaks in residential plumbing. Multiple studies were commissioned to identify the root causes:

· Initial Findings: Early assessments suggested that many leaks were the result of poor soldering practices or excessive soldering paste (flux) used during home construction.

· Investigative Breakthrough: A comprehensive scale analysis of harvested pipes revealed an absence of protective carbonate scales. It was determined that the "soft" nature of the local source waters made it difficult for plumbing to form the natural barriers needed to prevent pitting.

· Biological Testing: CCMWA tested for sulfate-reducing bacteria (SRBs) that could cause microbiologically influenced corrosion; however, results consistently showed no presence of these bacteria in the system.

Steps Taken to Reduce Corrosion in the Future

To address these findings and prepare for more stringent future regulations, CCMWA took the following proactive steps:

· Selection of Orthophosphate: After pilot studies compared various corrosion inhibitors, phosphoric acid (a type of orthophosphate) was selected as the preferred strategy. Orthophosphates work by forming a thin, sparingly soluble, protective layer inside pipes, significantly reducing the release of metals into the water.

· Treatment Plant Upgrades: Between 2022 and 2023, CCMWA received approval from the Georgia Environmental Protection Division (EPD) to design and install new chemical feed systems for phosphoric acid at both the Quarles and Wyckoff Water Treatment Plants.

· Gradual Implementation: To ensure a stable transition that would not disrupt existing pipe scales, orthophosphate was introduced gradually in 0.1 mg/L increments over eight months, reaching a target dose of 1.0 mg/L as PO₄ by late 2024.

· pH Optimization: Following the introduction of the inhibitor, CCMWA adjusted the target pH of the water from 8.0 to 7.7. This pH maximizes the effectiveness of orthophosphate in reducing lead and copper release.

Current Water Quality and Safety Results

The transition has been a success, with data indicating that the addition of orthophosphate is decreasing the rate of corrosion and metal release within the system.

· Lead & Copper Rule Compliance: 2025 system-wide sampling confirms that 90th percentile lead and copper levels remain well below current and future federal requirements.

· Continuous Monitoring: We utilize a dynamic dashboard to track water quality parameters daily at our treatment plants and monthly at distribution sites to ensure the system remains pH stable.

· Award-Winning Protection: In 2022, our plants received the GAWP Platinum Award for 13 consecutive years of full regulatory compliance.

Best Practices for Residents

While CCMWA treats the water to be as non-corrosive as possible, the primary source of lead and copper remains private household plumbing. We recommend these best practices:

· Use Only Cold Water: Always use the cold water tap for drinking and cooking, as hot water can increase the leaching of metals from your pipes.

· Flush the Lines: If water has been sitting in your pipes for more than six hours, let the cold water run for a few minutes before use until you notice a temperature change.

· Clean Faucet Aerators: Periodically remove and clean the small screens on your faucets to clear out any trapped sediment or debris.