Recycled water showed less toxicity than tap water in new study


A new Stanford University study shows that after treating potable reuse water, it can often be cleaner and more dependable than conventional drinking water sourced from pristine-looking rivers.

Many rivers have wastewater dumped in them with much less treatment than occurs in potable reuse systems, suggests the study published in Nature Sustainability. This leaves many contaminants, such as chemicals from personal care products and medicines, floating down river and straight into a drinking water plant.

Reverse osmosis treatment, however, pushes water at high pressure through a filter that’s so small, it squeezes out even sodium and chloride. It’s a process that cleans wastewater as much, if not more, than groundwater.

In other words, potable reuse — or recycled water — can provide a safe, energy-efficient and cost-effective alternative water supply, explained Stanford professor William Mitch, senior author of the new study.

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“There are additional benefits beyond a secure water supply,” Mitch said in an announcement from the Stanford Engineering department. “If you’re not relying on importing water, that means there’s more water for ecosystems in northern California or Colorado. You’re cleaning up the wastewater, and therefore you’re not discharging wastewater and potential contaminants to California’s beaches.”

A wider implementation of reuse water, however, remains hindered by uninformed public perceptions of potential health risks, adds Mitch. In Canada, a partnership between the University of Calgary’s Advancing Canadian Water Assets program and Alberta’s Village Brewery launched its Village Blonde Natural Golden Ale in 2020 as a way to shine a light on water scarcity and promote Alberta’s first wastewater-treated beer.

Other examples of water reuse in Canada include irrigation for golf courses and agriculture, as well as toilet and urinal flushing.

Regulators demand more extensive treatment at potable reuse treatment plants. They specify that treatment systems must remove harmful pathogens, such as viruses and amoebas, and utilities remove other contaminants using reverse osmosis, ozonation, biofiltration, and other cleaning techniques.

The study’s researchers gauged the toxicity of different sources of tap water by using hamster ovary cells that act similarly to human cells. Whether the cells slowed or stopped growing compared to untreated cells, helped to paint a picture about the effects of some chemicals. Tap water will carry residual disinfectant, for instance, to prevent pathogens growing in the pipes, said the researchers.

Mitch notes that disinfection is a balancing act between killing pathogens and minimizing exposure to harmful byproducts.

“We can’t get to zero contaminants. That would be ridiculously expensive, and probably unwarranted from a health point of view,” he said.

The engineers discovered the compounds regulated by the U.S. Environmental Protection Agency accounted for less than 1% of the harm to the hamster ovary cells.

In all of the study’s testing, the cytotoxicity of potable reuse waters was found to be lower than that of drinking water derived from surface waters, even in the absence of reverse osmosis.


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