By Rick Andrew
Has anyone recently heard concerns from consumers and other end users about lead in drinking water? Is the sky blue? Of course these days, lead contamination is one of the most prevalent concerns that consumers have regarding the safety of their drinking water. In fact, in 2016, about 40 percent of consumers who contacted NSF’s Consumer Affairs Office had concerns about lead in their drinking water. When you think about the wide variety of possible contaminants they could be asking about, 40 percent being related to one specific contaminant is a huge number.
Although there has been a recent spotlight on lead contamination, the issue is not a new one; lead has been a concern dating back many years. As such, the NSF/ANSI Drinking Water Treatment Units (DWTU) standards have long included requirements for lead reduction for filtration, RO and distillation systems.
All of these standards require that treatment systems must reduce a challenge level of 150 µg/L lead to 10 µg/L or below. 150 µg/L is representative of high concentrations in real-world public water supplies, although in extreme cases, much higher levels have been detected. Often these really extreme cases involve large particles of lead (such as lead solder) that have been released by old plumbing in the building and are captured in the collected water sample; there can also be other scenarios leading to extreme concentrations of lead being detected. 10 µg/L is based on the Health Canada maximum acceptable concentration for lead in drinking water. The US EPA action level for lead is actually 15 µg/L. In order to be more protective, the NSF/ANSI DWTU standards refer to the 10 µg/L Health Canada maximum acceptable concentration.
Lead in drinking water
Lead in drinking water can be either soluble (dissolved) or, as mentioned above, it can be in particulate form. The solubility of lead in drinking water is quite complicated, with various forms of lead being possible given variation in pH, levels of oxidizers (such as chlorine) and other possible water chemistry differences. Very generally speaking (other parameters being equal), at low pH, lead tends to be more in the 2+ oxidation state and more soluble, whereas at higher pH, lead tends to be more in the 4+ oxidation state and less soluble. Because it is possible for lead to be soluble or particulate—or possibly a combination of some soluble and some particulate—it is important that treatment technologies are able to address both.
The NSF/ANSI DWTU standards address filtration, RO and distillation technologies for lead reduction. Each of these technologies can be tested and proven to be effective in reduction of soluble and particulate lead. For example, filtration systems can include active media to adsorb soluble lead and have mechanical filtering capabilities through a carbon block, ultrafiltration or similar technology. RO can reject soluble lead due to the electrical charge associated with it and the membrane can also prevent particulate lead from migrating. Distillation vaporizes and condenses water, largely leaving soluble and particulate contaminants (including lead) behind.
Specific test methods
There are various forms of lead in drinking water and differences in how technologies treat that contamination. Each test method in the NSF/ANSI DWTU standards for evaluating the various technologies are specific to them, as defined below.
NSF/ANSI 53 includes requirements for evaluating filtration systems for lead reduction. It requires that lead reduction be tested at both pH 6.5 and pH 8.5. The test methods include very specific requirements for the test water, especially at pH 8.5. The pH 8.5 water must be formulated in a highly prescribed and detailed fashion to result in 27 to 33 percent of the lead being in particulate form, with at least 20 percent of the particulate lead being between 0.1 and 1.2 µm (microns) in size and the rest of the particulate lead being 1.2 µm in size or larger. In contrast, the pH 6.5 test is addressing lead that is completely soluble in nature. Successful testing at both pH 6.5 and pH 8.5 is required to establish a claim of lead reduction. The tests must be conducted to 200 percent of the manufacturer’s recommended treatment capacity or 120 percent if the filtration system includes a performance indication device (PID) that lets the user know when it is time to change the replacement element. Samples of the challenge water and treated water are collected at six points throughout the test to establish treatment performance.
Requirements for evaluating POU RO systems for lead reduction are included in NSF/ANSI 58. The test water for lead reduction for RO systems can be tap water meeting certain criteria for pH, TDS, turbidity and temperature, with lead added to the tap water to achieve the required 150 µg/L concentration.
The test itself is conducted over the course of a week, with various operational cycles to take into account several different possible operating conditions of a typical POU RO system. For example, for a typical POU RO system with a storage tank and automatic shut-off valve, there are operational cycles involving:
- completely emptying and filling the storage tank
- emptying the storage tank to the point where the automatic shut-off valve is activated and allowing the tank to refill
- drawing five percent of the daily production rate of the unit and allowing the tank to refill
- forty-eight-hour stagnation with no water drawn from the storage tank
Samples of the challenge water and treated water are collected throughout the test period at points where water is drawn from the storage tank. These samples are analyzed to determine the effectiveness of the treatment.
Distillation can also be an effective treatment for lead in drinking water. NSF/ANSI 62 includes requirements for evaluation of distillation systems for lead reduction. These requirements indicate that, based on the 1991 study, Evaluation of Total Dissolved Solids as a Surrogate Parameter for the Reduction of Inorganic Contaminants by Distillation Systems (conducted for the Water Quality Association by NSF International), TDS may be used as a surrogate for verifying the reduction of arsenic, barium, cadmium, chromium, copper, lead and selenium, when the system is tested for TDS reduction according to NSF/ANSI 62.
This test for TDS reduction involves test water prepared by adding sodium chloride to RO/DI water to a concentration of 1,000 mg/L. The distillation system must reduce the TDS by 97 percent over the course of the test protocol. The test protocol for distillation systems covers a one-week period, involving either batch or continuous operation depending on the operating characteristics of the distillation system. A stagnation period is included in the protocol. Samples of the challenge water and distilled water are collected throughout the test to establish the TDS reduction performance. Unlike filtration technologies, distillation effectiveness is not sensitive to the form of the lead. So, a claim of lead reduction may be made for systems that meet the requirements for TDS reduction under NSF/ANSI 62.
More than one way…
Lead in drinking water is a hot topic these days. Fortunately for our industry, there are various treatment technologies that can be used for water that may have lead contamination. And just as there is more than one way to treat drinking water that is contaminated with lead, there is more than one way to test the effectiveness. In each case for testing, a very high concentration (150 µg/L) of lead is included in the challenge water and the treated water must contain no more than 10 µg/L of lead. Rigorous test protocols take into account the treatment mechanism and operating characteristics of the treatment system to help ensure real-world effectiveness based on testing according to the NSF/ANSI standards. By testing products according to these protocols and requirements, manufacturers can help assure consumers and other end users who have these concerns about lead in their drinking water that the treatment systems will be effective, despite the complexities and variations that can occur with different real-world scenarios involving lead contamination.
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