Just wanted to add that it is possible to get bottled water w/o chemical junk in it. But, it still requires more caution than getting it at a LFS, even if the bottle says RO on it. I've found occasional bottles of distilled and RO that had kH readings that were enough to throw off my pH after repeated topoffs. I've never run accross distilled or RO bottled water with nitrate problems, just kH readings and high pH values (one bottle had a pH of 9.0 coinciding with a low kH reading). So, be cautious and also only buy the bottled water if it specifically states that it's distilled or RO somewhere on the bottle. If it doesn't say one of those, it could have chemical junk since there's nothing explicitly stating how it was filtered or if anything was added to it.