A Common Sense Approach to Residential PFAS Treatment

by Emily McBroom and Gene Franks

Most of the information now available about how to remove PFAS from water focuses on the gigantic carbon filters made to treat the millions of gallons of water per day required by cities.  Also mentioned are the very small residential drinking water filters, mainly carbon filters, that have received NSF certification for PFAS removal from drinking water.There is a lot of confusion about the residential applications that fall between the gigantic and the tiny.

Here are some things to consider about residential applications for PFAS reduction.

1. Consensus is that three treatment strategies work with PFAS: carbon filtration, reverse osmosis, and ion exchange. Of these, carbon (GAC) filtration seems most practical for municipalities. GAC and reverse osmosis both work well for residential users, with reverse osmosis an easy first choice for drinking water. One agency tested eleven separate undersink reverse osmosis units and found that they all removed PFAS well. Several pretty unassuming carbon filters have gained NSF certification for PFAS reduction.
2. Those who recommend treatment equipment for residential applications almost always make an unfounded assumption that homes must use point of entry equipment, treating all the water going into the home. We find no convincing information to indicate that PFAS in water is anything other than an ingestion issue.  According to the CDC’s Agency for Toxic Substances Disease Registry:   “Studies have shown that only a small amount of PFAS can get into your body through your skin. Therefore, showering and bathing in water containing PFAS should not increase exposure. Washing dishes in water containing PFAS should not increase exposure.”
3. For point of entry treatment, we found that almost all recommended treatments are simply scaled-down versions of the strategies developed for municipalities.  Usually there is no rationale stated that would justify the sizing recommendation. Recommended sizes range from extra large to even larger. We found EBCT (Empty Bed Contact Time) recommendations for PFAS ranging from 6 to 16.  Ten is a common recommendation. Using an EBCT of ten, to provide a modest service flow of five gallons per minute for a residential whole house filter for PFAS one would need almost 7 cubic feet of granular carbon.  That’s a 21″ X 72″ carbon tank, or three or four 12″ X 52″ tanks installed in series, or five 10″ X 54″ tanks installed in series.  One authority recommends “at least 200 pounds of GAC” for residential whole house treatment–a 7 cubic-foot filter array.  That’s a lot of equipment to assure PFAS-free water for flushing toilets. The most commonly suggested point of entry system is for two 12″ X 52″ GAC filters installed in series, without regard to family size. This would provide an EBCT of 6 at 5 gpm.
4. No one offers information about PFAS performance for whole house sized carbon block filters, although carbon block units might offer the most practical PFAS whole house option.

The Obvious Conclusions

Our advice to consumers is get an undersink RO unit. If you don’t want reverse osmosis, get a high quality undersink or countertop carbon drinking water filter with an ample amount of carbon, and service it regularly. Ignore PFAS as a point of entry treatment issue, but don’t drink water from the bathtub. Treat your drinking water well, and add a whole house carbon filter if you want to, but  you don’t have to get a box-car sized filter that competes with the city water department because if your drinking water is taken care of, a little PFAS in the shower water won’t matter.