I am trying to root a number of plants in plain water. This is about day 4 on most, if not all, of them. I’ve been checking the quality of the water each day. I found that almost all of them were developing a funk or mold around the parts that are in the water. To combat the funk, I dipped all cuttings in a 10% bleach/90% water solution, rubbing slightly to get any of the sliminess off. I then dumped whatever water was in the cups they had been sitting in, sprayed the inside of the glasses with the 10% bleach solution, returned the cuttings to their individual glasses, and added distilled water until it was about an inch above the bottom of the cuttings.
I am not sure whether this will be enough to keep the funk away, but I will continue to monitor and treat with the 10% bleach solution until the cuttings are either rooting or are dead.