So you may ask, why wouldn't I just use bottled water in an emergency? Bottled water (this applies to any water in a plastic container) has a maximum shelf life of 18 months. Don't believe us; check the stamp on the water that you get at your local grocery store. The plastic (high-density polyethylene, or HDPE) that makes up most bottles is porous, which means the water inside can pick up smells and tastes from its environment. The bottles are not hermetically sealed. So as water bottles sit, there will be some migration of chemicals from the plastic into the water.
These Emergency Purified drinking water packets are packaged in mylar and have a 5+ year shelf life. The military uses mylar for their food because of the prolonging shelf life properties