I was going through about a gallon of water a day per plant during heavy budding. Just something to think about, thats a lot of water to lug around every day. If you're that worried about stuff in the water just fill up a five gallon bucket and run a fish aerator into it for 24 hours if anything it will keep your water full of oxygen. Unless your water is so hard it's leaving calcium deposits you probably don't have anything to worry about. I grow massive rose bushes every year using the garden hose. There are trace minerals in water that may be benefical to your plants that won't be in the distilled water.