An inexpensive device for removing microorganisms from drinking water includes an Ultrafiltration membrane filter equipped with a pressure regulating mechanism to supply purified water to a suitable low-pressure reservoir equipped with a bi-directional hydrophobic membrane vent filter having a 0.01-0.05-micron pore size. The purified water may be supplied to the storage reservoir at a static pressure in the range of 1 to 8 pounds per square inch.