You really don’t wanna use soft water that’s had water softener additives.
I use tap, as long as you don’t have a ton of minerals that push your EC over .3 or so you’re fine. Mine is .2 out the tap, and that’s fine.
I use tap water. I used to use RO filter but I have a lot less deficiencies using plain old faucet water. My water comes out of the tap at around 120ppm and a high ph of 8+