Abstract: A compartment insert to be used in conjunction with a receptacle, such as a water bottle, that when inserted between and coupled with, the receptacle and its cover or lid, creates an enclosed, water-tight inner chamber that protrudes into the receptacle itself, and is suitable for storing contents of various types (e.g. personal items, snacks, drink mix, pills, electronics) and for various purposes (e.g. accessibility, convenience, consolidation of loose items, concealment, protection from elements, protection from physical wear). A user of the invention is able to open the receptacle and access its contents by removing the compartment insert while leaving the lid intact on the compartment insert and its contents remain sealed. The contents inside the compartment insert can be accessed by removing the lid while leaving the compartment insert attached to the receptacle, sealing its contents inside.