Household filter study - PFAS

Madison Water Utility continues to monitor all of our wells for PFAS, environmental contaminates that has have gained recent interest by health professionals, the drinking water community, and the public. While the levels found in Madison tap water do not warrant large-scale source water treatment, some residents wonder if household filters can further reduce the presence of these chemicals in their drinking water.

A recent study by Duke University and North Carolina State University analyzed the effectiveness of a variety of household filters at reducing PFAS from tap water. The two major types of filters studied were reverse osmosis and activated carbon filters. Here are some points that may be of interest to Madison residents.

Study Summary

  • In almost all cases, reverse osmosis and dual-stage (activated carbon-based) filters were able to reduce all analyzed compounds to below detection.
  • Dual-stage filters are under-the-counter filters that start with a sediment filter, followed by a granular activated carbon (GAC) filter.
  • Reverse osmosis relies on membranes with microscopic pores to filter out water impurities. The process can waste up to 3 times as much water as it filters. Therefore, on top of the costs to purchase and maintain these filters, households that use this type of filter will also be using more water.
  • Of the common household filters – faucet- mounted filters seemed to be the most effective. These filter types were able to significantly reduce PFAS of interest to Madison residents, including PFOS, PFOA, PFBA, and PFHxS, and next generation PFAS like GenX. In every case but one, they reduced each compound tested to below 1 ppt.
  • Refrigerator filter results were inconsistent due to variations in size from house to house. Larger fridge filters with more activated carbon were more effective.
  • Pitcher filters were reliable at reducing PFAS but not consistently to below 1ppt.
  • Single-stage under- the- sink filters were very effective at removing PFOS and PFHxS – however less effective at removing PFOA and GenX, and not effective at removing PFBA.

Bottom Line

Activated carbon and reverse osmosis filters can reduce PFAS levels in drinking water. If you want additional purity of your water, the right filter for your home and family will depend on your specific circumstances and budget. And remember, any filter used should be operated and maintained according to manufacturer’s recommendations. Change cartridges at the recommended intervals, and never put hot water through the filter.

Please contact Madison Water Utility’s Water Quality line for more information: (608) 266-4654

Original Literature: Assessing the Effectiveness of Point-of-use Residential Drinking water Filters for Perfluoroalkyl Substances, Environmental Science & Technology Letters (2020)

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