A compact filtering and additive delivery system which is readily adaptable to a portable container, such as a sports bottle, and receives a modular additive container for the metered delivery of additive, such as flavor concentrate, to a stream of base liquid as the base liquid is drawn or dispensed from the container. The modular additive container configuration on the delivery system allows a consumer/user to experience different additives, such as different flavors or supplement compositions, for a given supply of base liquid, such as water, stored in the container. The system may be readily used with off-the-shelf containers, such as disposable water bottles. An additive container configuration provides modular additive delivery system as described herein.