Geigerrig Hydration Engines, often referred to as "reservoirs" or "bladders", are compatible with most other packs. Pressurized to spray to cool, clean, share, and drink. Ready for Geigerrig plug-n-play, on-the-go, in-line filtration. Reversible reservoir that is dishwasher safe (top shelf). Really, it should be called a Personal Water System rather than a Hydration System. Why? Because a hydration system has come to be known as a plastic bag with a drink tube that can only be used for hydration for one person. The Geigerrig system dramatically expands the uses and access to water.