When I setup my first salt water (JBJ 12 Gallon) I was set on running it on tap water. Heck, I had been using tap water with my fresh water tanks for a couple decades with no problem...
Well, in my experience, it was not cool to do that (I had algae in all the wrong places BIG and FAST), and so within 6 weeks I had a RO/DI system running in my basement (<$300 all in from aquasafecanada). I had contemplated buying water and hauling it around, but after a quick discussion with my spine it wasn't going to happen
And I also bought a water cooler/heater at the same time, and we now use the RO water for drinking/cooking/etc which is far more healthy also!
(Edmonton's water is about 170-210 TDS)
Not really a direct answer, but my experience -- for salt water I won't use anything but 0 TDS water again. (if you are buying from a LFS or otherwise, make sure to test the TDS of it too before you buy
