I'm setting up my first saltwater tank. Its a JBJ 28g setup. I've been reading a lot. But I have one question about the water. I get R0 drinking water delivered to my house for the water cooler I have. Would it be alright to use this water with the saltwater mix. For water changes and topping off the tank. Thanks

Have you verified the purity of this water? I usually prefer water that has no detectable solids, but your drinking water source may be perfectly suitable, assuming it is free (or relatively so) of phosphate, nitrate, and other contaminants. A plain RO membrane is usually not very effective at removing certain ions, like phosphate and silicate, so there *may* be more in there than what you'd prefer.

Almost all of the water that companies like culligan sell is pure. Some of the other companies sell "spring" water and it is not always 0 TDS. Call Jim at the filter guys and he has some nice TDS meters so that you can test it... Everyone should have one anyways.

Some RO intended for drinking water is remineralized, you should check with the company to see if they add minerals back in for taste.
If it is straight RO it should be pretty good (90-98% pure) but RO/DI would be better. A $20 handheld TDS meter will tell you its condition.