RO water is what I use. I mix a gallon at a time, and put some in a spray bottle. The rest I use to submerge all my small equipment (hose, bungs, airlocks, spigot, gaskets, thief, autosiphon, etc.) in a 30" wallpaper tray. I use the spray bottle to coat the inside of my buckets & lids. If I'm bottling, I just decant a pint or so of the solution into the sulfiter (what turns out to be a "foam fountain" when used with Star San) and rapidly sanitize my bottles inside, placing them in the dishwasher for a spin through it.
That gallon can be used 3-4 times before the color of the pH paper goes off, and I just mix another batch. Very economical of water and Star San.