The lowdown on water:
1. Distilled water is the best. It is really pure. It has been boiled into steam (pure water since dirt & salts won't boil) and condensed back into pure water. This is the best water to use. Note, that if it is left open to the air, it will very slowly absorb carbon dioxide (what we breath out) from the air and become acidic (lower pH). Carbon dioxide (CO2) + water = carbonic acid, which is what makes bubbles in Coca-Cola.
2. Deionized water is your 2nd choice. Ions (like chloride & sulfate & fluoride) are always in tap water & many of them are corrosive. "Bad ions" are the main thing you don't want in your cooling system. Deionized water has had 99.99% of the ions removed. The downside to deionized is that they don't necessarily remove "dirt" from the water. I'm sure it goes through a filter & dirt is not really a big deal (compared to chloride, fluoride, etc. bad ions), but it's not as pure as distilled water.
3. Tap water - only use it if you're stuck by the side of the road. Tap water has a lot of bad ions in it and that varies city by city. In the Midwest, most tap water has carbonate (dissolved limestone). In the North, they have a lot of iron in the tap water (toilets get a brown ring in them from it). Many cities add fluorine for kids teeth or chlorine to kill bacteria. None of these ions are "good" and many of them are "bad ions" you don't want in your cooling system. The one rare exception is some new "trick" that Prestone is using in some of its new automotive antifreeze where one of their ingredients actually needs a little bit of "bad ions" to work at its best, but that is an odd-ball. Don't use tap water.
4. Well water - the worst water you can use. It is absolutely FULL of ions you don't want in your cooling system.
5. Dehumidifier water - not a bad idea actually. Because you're collecting water that was once steam/water vapor, it's almost like you have distilled water....but it will have a little air dust in it, so I'd rank it as a decent #2 choice for coolant water, equal to deionized, but behind distilled.