Regardless of the water source you use, you really should check it for nitrates and phosphates. I used to use tap water filtered with Britta, but found phosphates of 0.5 ppm. Algae...get ready, get set, GO! Sine this discovery, I have been using Glacier RO water from little refill stands outside Albertson's in California. Unfortunately, I have found that the RO water there has a 0.2 ppm phosphate level. If you don't want to put the $20 into a phosphate test kit, then at the very least, get whatever water you use checked for nitrates/phophates at your lfs (if the lfs is reliable).
sam