Water Quality

[horteco]

This is my 1st salt tank. My question is.
How important is it to have ro/di water?
The LFS says I've got a good water source, (city supply) soft, chlorine but no chloromines. LFS says I could just use "tap water conditioner" but I'm hesitant, the more I read the more confused I'm getting. Most sites insist ro/di water only. I don't want to start out on the wrong foot, but I dont want to spend $300 - $500 if I don't need to. Your suggestions will be appreciated.