Should be fine with any of the 55 gallon water barrels from 'prepper' suppliers, as long as they are made for drinking water, and haven't been previously used for anything. (Some sell used barrels that previously contained food grade products like fruit juice, which is not what you want.) Wash them out first to remove any dust or residue from the manufacturing process. Also look for the long-term stabilizer solutions they sell in small bottles, if you plan to store water for long before using. A hand pump attachment can be useful so you don't need to try to store them at a height off the floor to get good gravity flow, since they weigh so much when full. Store in a temperature controlled environment if possible, like a heated/cooled garage. Or at the least, don't let direct sunlight hit them if stored outdoors. Check trusted prepper websites that have been around for years, like survivalblog.com for more info, and recommended vendors.