A water purification system for purifying and storing drinking water, the system comprising: a pre-treatment stage for filtering untreated water to form pre-treated water, a three-way valve having an outlet and first and second inlets, each inlet having a flow regulator which regulates the flow of water into the three-way valve; a main treatment stage for treating pre-treated water by reverse osmosis or ultra-filtration to form treated water at a treated pressure; a storage stage for storing treated water in a storage vessel at a storage pressure which increases as the storage vessel is filled, the maximum storage pressure being less than equal to the treated pressure; wherein: the pre-treated water passes through the three-way valve in passage between the pre-treatment stage and the main treatment stage, the pre-treated water entering the first inlet of the three-way valve and exiting the outlet of the three-way valve; the treated water is separated into a storage stream connected to the storage stage and a recycle stream connected to the second inlet of the three-way valve; when the storage vessel is full of treated water at the maximum storage pressure, the first and second inlets of the three-way valve are closed; and when the pressure of treated water in the storage vessel is less than the maximum storage pressure, both flow regulators open until the maximum storage pressure is restored.