I think you're right Funkyman. I wouldn't trust that I was getting RO from a grocery store. You can buy some gallon jugs that say distilled and they will list RO as the type. My LFS charges .50 per gallon. That's why I took the plunge and got my own RO/DI unit. It'll pay for itself in the long run. Plus the cost of saltwater is .75 at my LFS. A bucket of salt will go a long way at those prices. I find I'm doing water changes much more regularly too.