Apparatus for storing water, especially purified water, for use in a beverage dispenser is provided with a microbiological agent to kill or deter microbiological growth and maintain the quality of the water. The agent is provided in a physical form to promote contact with the water and may be renewable to maintain effectiveness of the agent over a period of time. In one arrangement, the agent is contained in a cartridge 92 arranged in a re-circulation loop 89 through which the water in a reservoir 80 is passed and returned to the reservoir 80. The cartridge 92 and/or a carrier for the agent within the cartridge 92 may be replaceable to renew the agent. The agent may also be provided within the reservoir 80 and various arrangements for this are also disclosed.