Tap water is just fine. distilled water may have some copper depending on how it was distilled.
Um...NO. Tap water is NOT just fine as it contains countless elements that are bad for saltwater fish. Not only can these things independantly harm you fish, but they can add to your nitrate problem as well. And, as seen in beaslbob's other posts, he is having trouble with his nitrates.
Distilled water removes much of the garbage in tap water (which is OK for human consumption, just not marine fish). RO/DI water is best, but distilled is OK for the time being until you buy an RO/DI unit. IMHO.