I use jugs of RO water for brewing, but those do get boiled after the mash.
I might just be paranoid, but if I was storing yeast in the water, I'd boil. You go to a lot of trouble to do yeast washing/slanting and it'd be worth boiling the water. Of course, I also boil the jars and equipment to keep it as sanitary as I can.
Broken Leg Brewery
Giving beer a leg to stand on since 2006