The invention described herein is a modular water bottle system comprising an inner bottle, where an outer shell, further comprising an open top portion and an open bottom portion, fits around the inner bottle, where a base member is removably threaded onto the outer shell bottom portion, and where a cap assembly is removably threaded onto the outer shell top portion, where a sealing ring positioned around a neck of the inner bottle press seals against the an inner surface of the outer shell when the cap assembly is threaded onto the outer shell top portion. A design insert may be positioned between the inner bottle and the outer shell.