Composite membranes having a film of poly(ethenol) (polyvinyl alcohol; PVA) adhered to a microporous sheet of polyolefin are disclosed. The microporous sheet is made hydrophilic by grafting of the polyolefin, e.g. poly(ethylene), with a preformed polymer before adherence of the film of PVA. The composite membranes are chlorine tolerant with high levels of protein rejection making them particularly suitable for use in the extraction or recovery of water from feed streams in the beverage and food industries, including dairy.