Methods and systems are provided for modifying a fluid for oral administration. Typical systems include a reservoir which contains or may be filled with water or other aqueous components. The systems also include a container or retention pocket which is integral with or mountable on or in the reservoir. The container holds a soluble beneficial agent, typically an electrolyte, a nutrient or a medicament. The container is adapted to selectively combine a measured amount of the beneficial agent with the aqueous component based upon patient need.