How they work
The best methods to scrub PFOS and PFOA out of drinking water are filters that use granular activated carbon (GAC), ion exchange resins or reverse osmosis systems, according to the US EPA.
GAC filters use a layer of carbon to trap the forever chemicals as water passes through them.
They are an affordable option that is easily available, but their effectiveness can be highly variable. A study by Duke and North Carolina State universities found some brands of GAC filters completely remove forever chemicals, while others made no difference at all.
Ion exchange resin filters are similar to GAC filters, but are usually more expensive to purchase.
Instead of carbon, they use tiny beads that act like a powerful magnet to draw contamination from the water.
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Reverse osmosis systems force the water at high pressure through an extremely thin membrane that separates chemicals from the water. They require adequate water pressure in the pipes, so they may not be an option in homes with low water pressure.
Research from Environmental Working Group, a US non-profit environmental and health advocacy organisation, found these systems are the most effective at removing the contaminants, but they are also the most costly.
Maintenance is important for all types of filters, as they can become less effective over time as more contaminants accumulate in them. Carbon and resin filters have to be replaced more frequently than reverse osmosis filters.
The best way to choose a filter that will be effective is to look for one that has been certified by an independent third party.
Reputable third-party testing organisations include the National Sanitation Foundation (NSF), Water Quality Association (WQA) and International Association of Plumbing & Mechanical Officials (IAPMO), according to website Consumer Reports.
A product certified for PFAS reduction by the NSF group would be listed on packaging as “NSF/ANSI 53” or, for reverse osmosis systems “NSF/ANSI 58”.
If you buy an under-the-sink filter, don’t forget to flush it for at least 10 seconds to remove the build-up of bacteria trapped by the filter.