A new study shows that while activated carbon drinking water filters are capable of removing heavy metals like lead and disinfectants like chlorine, they may actually increase bacterial concentrations in filtered water. The study was conducted on Ann Arbor, Michigan, city water and showed that “filters significantly alter the bacterial abundance and composition of drinking water.”
In an interview with Michigan Radio the study’s author, Nancy Love, said it’s not clear what, if any, threat the bacteria pose to people. “The count of the bacteria coming out of the filter increases relative to what was going into the filter. And we see that those counts can increase up to 100 times. It doesn’t mean the bacteria are harmful. There are a lot of, you know, there are bacteria in drinking water and they’re completely harmless.”
Love went on to explain that bacteria that are harmless to healthy people could be dangerous to anyone with a compromised immune system. “We haven’t proven that part yet, but what the study suggests is that we need to take a closer look at these filters and different waters and see whether or not that is occurring or can occur,” says Love.
Anyone using a water filter should regularly change cartridges by following the manufacturer’s recommendations. Love said it’s also a good idea to flush out water pipes each morning to clear out bacteria that grow in pipes overnight. “So when you turn your faucet on first thing in the morning, that first slug of water that comes out will have higher bacteria counts than if you let it flush for a bit of time,” Love says.
In her interview with Michigan Radio, Love recommended “turning your filter onto bypass, and flushing for 15 to 30 seconds before turning the filter on, and then running water through the filter for five to 15 seconds before drinking it.”
The water filter study was published in the journal Environmental Science: Water Research & Technology on July 6, 2017.
Related water safety
- How to test water for lead in your home.