Abstract: A water purification apparatus utilizing a reverse osmosis cartridge which supplies a measured amount of potable water to substantially fill an open top pitcher of known desired size. This free-standing apparatus includes an electric pump which withdraws water from an overhead reservoir and pumps it through prefilters and the reverse osmosis cartridge, from which a brine stream returns to the reservoir and a product water stream discharges from an overhead outlet above the pitcher. Control means monitors the level and quality of water in the reservoir and halts the operation of the pump as soon as the water level falls below a lower predetermined level which is set so that the desired measured quantity will have been delivered to the pitcher from a full reservoir. The control means also halts operation when the total dissolved solids content in the reservoir reaches a preset upper limit.