Just casually go in and ask to see a TDS
reading of their RO
water. If they don't even have a TDS
meter to do it for you, then you can gracefully point out that the water they're selling has 40ppm nitrates in it when you get it home. Two things that will do... (1) establish whether the source water is the culprit, and (2) if it is, then the discussion will probably end right there! I can't imagine any LFS
trying to argue that 40ppm out of an RO
Before getting toxic on the LFS
, you should probably make sure it's indeed their water, and not contamination from your buckets or something that happened to the water once it left their shop.