call me old fashioned but I always used cold tap water. our local tap water is really good though, not like some towns. when I very first started shooting up (heroin at the time though, not pills, only switched to dilaudid and M100s after I moved and in the new location H was scarce, comparatively low quality and expensive) my always paranoid boyfriend insisted we boil the tap water first but we quickly fell off w/ that. if I was feeling particularly health conscious I would get a bottle of tap water from my pill dealer's house while there because he had some super filter on his tap that he insisted "made the water perfect for shooting up with" and he would never use any other water ...he was in his 70s had been a junkie for probably longer than even my parents have been alive and still had veins left so I took him at his word. xP I IV zubsolv (and no it doesn't do shit in way of effects, I just have a bad needle fix, whatever) these days and when IVing any buprenorphrine or sublingual tablet in general you MUST use saline solution, because the form that the drug is in is not a salt, so it is like shooting pure water into your veins. I lost so many veins for good before I realized this, shooting up zubsolv w/ purified bottled water (ugh) no less because at the time I lived on a property w/ beyond shitty well water, pretty much entirely undrinkable not just because of the rotten eggs sulphur and overwhelming iron taste but because all the iron in it would start causing you to have frequent nosebleeds if you drank it every day for a while, I never would have shot up w/ that shit even though my only other choice was the obviously less than ideal purified bottled water. shooting up most pills I would think it best (if unable to access sterilized water as mentioned above, not a ton of people have access to that), that boiled tap water would be best, then cold tap water (I am under the impression that using hot tap water is less than ideal because bacteria can grow in the water heater tank particularly because the heat of the water is enough to encourage bacteria growth, not enough to actually kill bacteria), and if there is no other option bottled water. I would not ever inject w/ anything else. I did not look at that water choices safety list thing that was linked so I may be wrong (will look at that when finished posting because I am indeed curious), but this is always what I've believed based on what I know. also I have always thought it best to use as little water as you need to dissolve the pill completely, because you do not not want to be shooting up a really "watery" fluid, that is you want the salt concentration to be high enough that it does not cause extra damage to your veins and kill your blood cells.
just my experience and opinion.