Well, I'm going to be frank here.
This hobby isn't cheap, if you're looking for the cheap way around things, you're going to have lots of issues and dead critters. I say this even more so because you are new to the hobby and don't know you're way around things to do shortcuts.
You need to buy bottled water, buy RO/DI from a LFS or get an RO/DI unit, OR have issues.