available with three fundamental approaches: A "bare bladder", intended to be carried in a matching pocket of a "hydration-system compatible" backpack. (Such a pack will usually also feature a hole through the pack, near the upper anchoring point of the pack's shoulder straps, sized for the hose and bite valve to pass through it, and often covered by a flap that prevents rain entering the pack through it.) As part of an integrated design incorporating both a backpack and the hydration system (usually sold together as a hydration pack), usually with at least a few pockets-worth of storage space for other items. (Such a combination is likely to have a channel inside one or both shoulder straps, for the hose to pass through, preventing the hose from tangling with other gear or the environment, and ameliorating the annoyance of the liquid warming up while waiting in the hose to be drunk next, or the problem of it freezing.) A basic hydration system in a protective fabric shell, so that the bladder is unlikely to be damaged by other gear that it shares the interior of an ordinary pack with. (The CamelBak brand products of this kind are trademarked as "The Unbottle", for instance, and each looks a lot like a very small pack, with a hand-carrying strap at the top and four D-rings that could facilitate attaching it to the outside of a pack. However, they completely lack shoulder or waist straps.) Accessories Some manufacturers offer parts for replacement or customization, whether compatible only with their own hydration systems, or usable also with others'. Plumbing Shut-off valves Especially while a hydration system is being carried in a vehicle, there is some danger of the bite valve being squeezed, opening it to leakage or a steady flow; this can be guarded against with an additional valve, usually installed between the bite valve and the hose, that stays open or closed according to the position of a lever. Elbows The bite valve may be installed with a right-angle extension between it and the hose, to achieve a preferred positioning and angle of the valve relative to the user's mouth. Hose anchors Position and angle may also be adjusted by clips that clip usually to a pack strap and (for instance by clipping to the hose, or looping around it and snapping to themselves to close the loop) control the hose's path Insulation