I was at Nathan's today, he doesnt have one, not to say he could not order one from somewhere, but i can do that too. I called Big Al's in London, and they also have to order one. I have lost faith in my RO supplier when i called and asked if he sold them and he didnt really know what a TDS meter was. I have an old Kent Marine RO/DI machine and new filters, Just not a new RO membrane. I wanted to test it to see if I needed to get a new one or if it was still good. I can get one online for about $20.