Originally designed for laboratory work, Whirl-Pak bags make great emergency water collection, purification, and storage bags, and are also great for storing food. They're completely sterile and food-safe, and will not leach harmful chemicals into your water or food supply. They are shipped sealed; you can always tell that your bag is completely sterile and has never been used, since you have to remove a perforated tab prior to use. Each bag has a writable area for you to add notes ("non-potable" for instance). Whirl-Pak bags are ideal for survival kits, because they roll to very compact dimensions, weigh very little, and are incredibly tough. Several US Military Kits specify Whirl-Pak bags for emergency water collection, treatment, and storage. They can even be used to make an improvised solar vegetation still. The 4.0 mil wall thickness means that this is a durable bag, extremely resistant to puncture or tearing. These bags stand on their own thanks the gusseted bottom construction. This means you're unlikely to spill precious sterilized water. They are safe for use with chlorine tablets, iodine tablets, or UV purification systems.