depends on what your regular water is like to start with. I use water right outa the tap and have basically no problems. Other peeps have horrible tap water and use RO or bottled water. If using RO, bottled or even rain water(I believe) your going to be missing alot of trace elements which are either not there or are removed during whatever process your doing (RO). If using alternative water you most likely will be needign Calmag as an additive along with your nutes