the good thing about RO water is you know what's in it, which should be nothing. Other kinds of water have micro nutrients in them for example, fluoride and calcium for tap water, and carbon and magnesium for mineral water. Upping you PPM synthetically by using something else than RO will work for sure, but are they good PPMs? that's the main question, and why you don't want to up your PPM simply by switching to a different kind of water. If you do, and you want to spend $ on water, mineral water has loads of Carbon and minerals in it, that could be a good thing. think about adding some CO2 if you can, in veg it's very important indeed !