Abstract: A method and apparatus of purifying contaminated liquids employing a particulate filter and a membrane in combination. The particulate filter and membrane are disposed in a unitary container with the membrane being located downstream of the particulate filter. During the process of purifying a contaminated liquid, the membrane causes a back pressure to be exerted on the particulate filter thereby providing substantially even flow of liquid through the particulate filter and minimizing problems associated with uneven flow such as channeling, piping, purging and tunneling. An improved method for cleaning the liquid purification apparatus is also disclosed. The cleaning method preferably employs a gas such as air for scouring the particulate filter and the membrane in a single operation.