reverse osmosis (RO), helps us get drinking water that stays clean and stable for longer. What we didn’t know much about was how RO water affects biofilms and the growth of L. pneumophila, the bacteria that causes Legionnaires’ disease. So, we set out to do two things: first, figure out how much Legionella could grow in RO water, even after we added minerals back in, and compare that to regular treated groundwater. Second, we wanted to see if different pipe materials, when exposed to remineralized RO water, could still encourage L. pneumophila to grow.
We used a boiler biofilm monitor (BBM) to check the water’s Legionella growth potential. This monitor really mimics how water flows in a home plumbing system. For the materials, we used a biomass production potential (BPP) test. We measured ATP levels in the biofilm on glass rings from the BBMs. With RO water, those ATP levels hovered around 100 pg ATP cm-2. But with conventionally treated water, the ATP concentrations in the biofilm were ten times higher! Not only that, conventionally treated water had a Legionella growth potential that was a whopping 1000 times higher than RO water, even after remineralization. When we looked at the BPP-test, glass, copper, and PVC-C showed the least biofilm and Legionella growth. PE-Xb, PE-Xc, and PE-100 were next, and PVC-P had the most biofilm and highest Legionella growth potential.
So, what does this all mean? Our study clearly showed that remineralized RO water doesn’t make L. pneumophila grow more in plumbing systems. However, if you’re using PE or PVC-P pipes, you might still see L. pneumophila growth, even with high-quality RO water. It’s something to keep in mind when you’re building or updating your water systems.
