Nationwide, lead solder is the dominant source of water lead in many buildings and residences. In some circumstances, its corrosion is known to be strongly influenced by sacrificial coupling to copper pipe. Free chlorine was recently discovered to trigger the electrochemical reversal of copper and lead pipe galvanic couples, making lead cathodic to copper and reducing lead release. This has not yet been shown for lead solder. Herein, we report the first chlorine-induced electrochemical reversal of the copper and solder (50:50 Pb:Sn) galvanic couple. After ~8 months in continuously flowing rigs, the electrochemical potential of lead solder rose steadily in the presence of chlorine, but not chloramine. After removing simulated lead solder:copper joints from continuous flow, lead release during stagnation was determined. Two-thirds of the chlorine-treated joints had >2 orders of magnitude lower lead release (<6.0 ppb) than similar copper joints treated with chloramine (2060 ppb) at the same pH. These simulated joints with low lead release demonstrated potential galvanic cell reversal during stagnation, with the lead solder surface corrosion potential (+138 mV) slightly exceeding that of copper. The average solder surface corrosion potential of chloramine-treated coupons (-186 mV) was always anodic to copper. The solder surfaces of only the chlorine-treated coupons formed a dark film, possibly a Pb(IV) scale. These findings may help clarify prior case studies demonstrating profound reductions in lead release for free chlorine versus chloramine, which heretofore defied explanation. This work has profound implications for corrosion control and reduction of lead in public water supplies.

One water utility’s 90^th percentile lead levels increased from non-detect to 131 ppb after switching from a low-nitrate groundwater to a high-nitrate surface water. Lead release was attributed to lead solder corrosion and was significantly correlated with nitrate in both field data (p=0.003) and complementary laboratory experiments (p<0.001). Under some circumstances, nitrate attacked the bond between solder and copper pipe, causing the erratic spalling of very large pieces of lead solder (up to 7 mm in length) and creating an acute health risk. To date, there is virtually no research on nitrate’s effect on solder or associated corrosion control guidance. Here we identify a novel mechanism by which nitrate oxidizes lead solder via formation of ammonia at relatively low pH resulting from galvanic corrosion.

Scanning electron microscopy was used to assess the composition of solder surfaces from the laboratory studies and harvested pipes from the affected community. Nitrate appeared to selectively attack the tin in solder and this detinning was most evident where solder pieces spalled off. Follow up studies involving galvanically coupled copper and lead-tin alloys demonstrated that spalling and solder surface fragmentation depended on alloy tin content. This attack appeared to be worst for 50:50 lead-tin alloys that were widely used to solder plumbing prior to 1986. This work is important given that nitrate is increasing in some drinking water supplies, and more utilities are switching water sources for a variety of reasons including improved sustainability.

Drinking water quality standards are not monitored by the U.S.EPA beyond the point-of-entry of buildings. Building plumbing consists of pipes, water heaters, fixtures, and other components often associated with high surface area-to-volume ratios, long water age, and great temperature ranges. Those factors can contribute to water quality deterioration by increasing the rate of disinfectant residual decay and creating conditions for the amplification of opportunistic premise plumbing pathogens (OPPPs). Exposure to OPPPs, such as Legionella pneumophila, can occur through aerosol inhalation during water usage events in buildings and may cause respiratory diseases to immunocompromised individuals. Controlled studies to evaluate response of OPPPs to operating conditions associated with hot water systems are lacking and can support development of best operating practices and building water management guidelines.

To evaluate the response of OPPPs to water use pattern, temperature, and physical/chemical water quality parameters in electric storage water heaters, a new laboratory facility has been built at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. Water samples from the top, bottom, and influent line of the heaters have been collected to quantify OPPPs of concern (Legionella pneumophila, Pseudomonas aeruginosa, Mycobacterium avium, Naegleria fowleri) as well as the genus Legionella and Mycobacteria through digital droplet PCR. Disinfectant residual concentration, pH, turbidity, conductivity, hardness, and heterotrophic plate count levels have also been measured in the samples. Temperatures within the tanks have been monitored daily along its vertical profile. Details of the laboratory setup, experimental design, research questions, and results will be presented.

The drinking water-associated opportunistic pathogens Legionella, Pseudomonas, and nontuberculous mycobacteria cost the US $2.39 billion annually. Disinfection by-products and heavy metals in premise plumbing water supplies also pose serious threats to public health. Modeling approaches to prevent conditions conducive to premise plumbing water quality degradation have typically focused on individual contaminants or pathogens. Accordingly, a variety of models at the pilot, bench, and occasionally field-scale have been developed. However, practical barriers exist for using real-time models for managing water quality in buildings.

To work towards a harmonization of mechanistic and data-driven modeling approaches to forecasting premise plumbing water quality, a combination of literature-based risk models, machine learning models, and two long-term field studies were conducted in sustainable Leadership in Energy and Environmental Design (LEED) buildings located in Arizona. Sensor measurements for common water quality parameters (pH, chlorine, and conductivity), as well as grab samples (disinfection by-products, heavy metals, and the opportunistic pathogen Legionella) were used to understand physical-chemical and microbial water quality in the buildings prior to, during, and after flushing and water heater set-point interventions. Risk trade-offs in intervention strategies were identified, indicating a need to holistically manage water quality. Additionally, expansion tanks and water softeners were identified as understudied sources of Legionella contamination. Machine learning models applied to sensor data indicate that propagating model error is key for incorporating into building water quality models. This integrated modeling and field work identifies key logistical barriers and research gaps to inform future proactive water quality management efforts.

This study was conducted to address significant knowledge gaps regarding the drivers of heavy metal fate within plastic potable water plumbing materials. A systematic investigation was conducted to examine the mechanistic role of biofilm presence on lead (Pb) accumulation onto crosslinked polyethylene (PEX-A) and high-density polyethylene (HDPE), and copper potable water pipes. Three pipe loops were constructed and biofilms were grown on the inner surfaces of these pipes for three months. Biofilm biomass and the pipe surface charges were quantified using ddPCR and zeta potential measurement, respectively. Pb exposure experiments were conducted for five days under flow and stagnant conditions, and the influence of initial Pb concentration on Pb deposition rates onto the new and biofilm-laden water pipes was examined. The results showed an increase in biofilm biomass on PEX-A pipes compared to HDPE and copper pipes. The biofilm presence on HDPE pipes resulted in slightly more negative zeta potential for HDPE pipes than pipes without biofilm. Biofilm-laden PEX-A and HDPE pipes accumulated more than three times the Pb loading than new PEX-A and HDPE pipes after a 5-day exposure period under stagnant conditions, while no significant changes occurred for the copper pipes. A lower Pb accumulation on biofilm-laden plastic pipes than on new pipes under flow conditions was found. A pseudo first order kinetic model best described the Pb accumulation onto the new and biofilm-laden water pipes. Pb accumulation rates were greater for biofilm-laden water pipes compared to new pipes under stagnant conditions.