Proactively evaluating the impact of source water changes on lead–tin solder corrosion

Lead in drinking water is often discussed in the context of lead service lines, but for millions of homes built before 1986, lead–tin solder in copper plumbing can also be a serious source of exposure. As utilities adjust treatment strategies or change source waters to meet new regulations, improve sustainability, or respond to groundwater contamination, shifts in water chemistry can unintentionally alter corrosion behavior inside customers’ homes.

That’s the focus of a recent paper in ACS ES&T Water, “Proactively Evaluating the Impact of Source Water Changes on Lead–Tin Solder Corrosion,” co-authored by Carollo’s Kathryn Lopez. The study challenges “common sense” assumptions about lead solder corrosion, and offers a practical bench-scale approach utilities can use to evaluate risk before a major water change reaches the tap.

Why Source Water Changes Can Increase Lead at the Tap

Utilities rarely change water sources lightly, but it’s happening more often due to climate pressures (like salinization and saltwater intrusion), new treatment needs, or system consolidation. The paper emphasizes a key lesson: it’s not just today’s water chemistry that matters, it’s the home’s corrosion “history.” In one “worst-case” scenario described in the study, decades of noncorrosive water preserved lead solder in a relatively pristine condition. When the home later received more corrosive water, the preserved solder became vulnerable, leading to chunks of solder breaking free and yielding very high lead results.

As the authors note, “conventional wisdom regarding lead–tin solder corrosion problems is inadequate,” especially when water changes introduce new corrosion conditions.

Lead Solder Corrosion Can Behave in Unexpected Ways

A major takeaway is that lead solder corrosion is not always a slow, steady dissolution problem. The paper highlights the release of particulates, where lead-bearing material can detach intermittently, creating “spiky” sample results that are difficult to predict and even harder to capture with traditional sampling methods. The research also highlights that galvanic corrosion (occurring when lead solder is connected to copper) can behave significantly differently from lead in other forms. In some cases, lead release from solder connected to copper can be far higher than from lead pipe coupons, even though the total mass of lead in solder is smaller, because the corrosion mechanism is different and can be accelerated under certain water chemistries.

Case Studies Show Desktop Predictions Can Miss Real-World Risk

The study compiles multiple case studies where desktop evaluations and existing assumptions failed to predict lead increases after a water change. A repeating pattern emerged: a community’s existing water appeared “safe” based on historical lead monitoring; a source water change (or the addition of a small area to an existing system) introduced different chemistry, often involving higher chloride-to-sulfate mass ratio (CSMR) and/or nitrate; and homes with previously preserved solder experienced sudden, high lead release, sometimes reaching the thousands of ppb in individual samples.

One striking bench test result described in the paper showed lead release jumping dramatically when coupons previously exposed to a noncorrosive groundwater were switched to a higher-nitrate surface water, illustrating how a change can “activate” a reservoir of still-intact solder.

A Practical Bench-Scale Testing Protocol Utilities Can Use Proactively

One of the most useful contributions is a short-term, three-week bench-scale testing protocol designed to help utilities evaluate proposed water changes before implementation. In simplified terms, the approach involves lead–tin solder/copper in current (in-use) water, then switches to the proposed new water with or without corrosion control options, and finally tests “worst-case” seasonal chemistry (such as elevated chloride and nitrate) to assess how lead release responds. This type of testing can help utilities identify high-risk scenarios early, especially where corrosion control strategies may reduce risk, or where a planned change requires additional safeguards and monitoring.

What This Means for Utilities Planning Corrosion Control and LCR Compliance

With lead service line replacement accelerating under the Lead and Copper Rule Improvements, many systems will increasingly focus on other lead sources, including lead solder and leaded brass. This paper is a timely reminder that low lead results in historic sampling can be misleading if solder reservoirs were already depleted in the homes being sampled. It also shows how source water changes and new treatment processes can shift chloride, nitrate, and CSMR, altering corrosion behavior in ways that are difficult to predict from theory alone. Proactive testing and targeted monitoring can reduce the chance of being surprised by lead spikes after a change.

To dive deeper into the case studies, the proposed risk framework, and the three-week bench-scale testing method, read the full article in ACS ES&T Water.