this is good advice and very informative. my barrels are brand new and already sanitized, so I will fill with water and then add the purifier to keep it fresh. store out of the sunlight or you will grow algae. water storage is very important. I live in a wildfire and earthquake danger area. now, after the fires of 2017, California is in the rainy season and we are having mudslides, rock slides and that blocks the highway to any city. if you don’t have supplies on hand, you may suffer shortages. always good to have water (most important!) and food storage. please read this author’s ideas in the link.