Hydro-3 has been designed specifically as an active riding pack with our unique Quadloc harness system. Providing a level of fit and comfort unequalled by any other hydration system. With a fully adjustable back-length and unrestricted underarm movement. Once set, the pack is exceptionally convenient to use, with none of the harness strap re-adjustment necessary on conventional harness systems. The adjustable back also allows the pack position to be moved up to allow large waist packs to be also worn. Hydro 3 can be worn with or without a waist strap - we recommend to use a waist strap for maximum stability, when carrying the full 3L (100 oz) water capacity.