I'm not even sure how water can dehydrate someone... That's like saying eat 80 cheeseburgers and you'll still be hungry.
Distillation, reverse osmosis are processes to remove minerals, contaminants and impurities from water.
Distilled is probably the best you can use for your plants. It's pure H2O, and contains nothing else. THEN you add nutes to your water. So then you have a perfect nute solution. I can tell you flat out exactly how much cal-mag, iron, boron, phosphate is in my water because it's written on the bottle and I use distilled (0) ppm water.
Tap water is by far the worst. That is basically filtered shit and piss water so they have to use an ass ton of chemicals to get it to be drinkable. Depending on the water and wherever your city pulls fresh water from ppms can be anywhere from 100-700+
