Bottle cages are designed to keep your water bottle with you at all times, regardless of what terrain you might be. Bicycles Online carry affordable alloy bottle cages (from brands like Zefal and Topeak), super light-weight carbon bottle cages (like the Elite Paron Carbon), everlasting composite bottle cages (like the Elite Custom Race), and adjustable bottle cages to fit a variety of different bottle sizes.  All bottle cages have standardised holes to fit all bike frames.