Yes, water that is very close to 0.0 EC/PPM, whether from distilled, a zero water filter, or a reverse osmosis filtration system, is ideal.
In this way, you know exactly what you are giving your plants. No extra calcium, iron or sulfur from tap water, as too much of these can cause nutrient lockout of other needed nutrients for the plants, especially with hard water, which will also raise your pH to unwanted levels.
You can use hard water, as long as the hardness is almost only made of calcium, and not much above 100 ppm and better yet if it is closer to only about 50ppm, but it can still throw off your pH, and it can make things more difficult because the ppm numbers from your tap water will be added to the recommended numbers for your nutrients, and you have to correct the high alkalinity/pH of the hard tap water.
If you think about it, the reason the hard water leaves “limescale” deposits on your faucets and such is because it isn’t much different than a liming agent, horticultural lime, which will also raise your pH.
Most of the time, I see most people use about 1,200 ppm of nutrients in their nutrient mix for their soil or soilless plants, in the common USA 0.5 conversion from EC. And so if your tap water has a starting PPM of 200ppm, then you add nutrients until you reach 1,200ppm, well, depending on the nutrient formula, that might mean you end up with too much calcium, iron, or sulfur, and maybe not enough of the other things like nitrogen(N), phosphorous§ and potassium(K), if you see what I’m saying. You might be able to go up to say 1,400ppm to make sure you have the recommended NPK ppm, but again, then you might have way too much of the things that are in tap water and then maybe you have too much calcium, iron, or sulfur.