After high-profile water crises like the one in Flint, Michigan, some Americans distrust the safety of their tap water, choosing to buy drinking water from stand-alone water vending machines or kiosks. However, this more expensive water may contain different contaminants than local tap water, according to a study in the ACS’ Environmental Science & Technology. Researchers report that water sampled from 20 stands in six states sometimes contained lead at levels higher than public health recommendations.
Currently, water kiosks are not regulated like tap water. Their water is not tested for lead or other metals. Updating water kiosk regulations can improve their quality and help consumers make informed decisions about the water they drink.”
Samantha Zuhlke, corresponding author of this study
Water kiosks are proprietary vending machines often marketed as safer than tap water, priced at $0.25-$0.35 per gallon (compared to less than 2 cents per gallon for tap water in most US cities). Booth operators generally treat local tap water with purification techniques such as filtration, UV light, or reverse osmosis (RO) to remove potentially harmful contaminants such as lead, microbes, residual disinfectants, and per and polyfluoroalkyl substances (PFAS). But automatic water vending machines in the US are not well regulated. Thus, a team of researchers led by Zuhlke and David Cwiertny conducted a comprehensive comparison of the chemical and microbial characteristics of water from the kiosks and tap water from municipalities near the monitored kiosks.
The team collected water samples from 20 stands operated by four different manufacturers in Iowa and the surrounding states of Illinois, Kansas, Missouri, Arkansas and Oklahoma. Most of the booths advertised their water treatment with RO, a process that uses pressure to force water through a semi-permeable membrane, purifying the water and leaving most contaminants trapped behind the membrane. For comparison, the researchers collected tap water samples from community sources within a mile of each stand.
They analyzed all the samples and found no evidence of microbial contamination in any sample. They also found that RO treatment in the booths effectively removed most PFAS from the tap water. However, this benefit was offset by lead levels in some RO-purified booth water samples—nearly twice the concentration recommended by the US Environmental Protection Agency.
The researchers found a lead in the corrosion of brass plumbing fixtures in the stands after RO treatment. Although plumbing fixtures are marketed as “lead-free,” small amounts of the metal can leach out under the low-pH, low-alkalinity conditions of RO-treated water, they say. Replacing the internal metal pieces with other materials could eliminate lead in the distributed water.
“This work adds to growing evidence that allowable lead levels in ‘lead-free’ plumbing may still be problematic sources of lead in drinking water when such plumbing is exposed to certain types of water, such as that created after RO treatment,” says Cwiertny.
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