I fill up water jugs from my tap and let them sit for a couple days before using them. I've checked the water here a couple times and the pH was fine. Pretty good water here in Vancouver. Trace minerals, no fluoride.
The main reasons I didn't add anything else to my plants is they didn't seem to need anything. Each time I could have given them something, they seemed healthy and happy, so I didn't. I've done a lot of fully organic tomato gardening in the past, so I figured my skills would translate over, and apparently they did.
There are lots of smaller reasons I appreciate too, like not having to 'flush', and never wondering what that funny taste in my medicine is.