A filtration system includes a vessel for housing at least two filtration elements. One or more of the filtration elements is a reverse osmosis membrane or a nanofiltration membrane and one of the other filtration elements is a microfiltration or ultrafiltration membrane. The vessel has an inlet port for providing a liquid feed to the filtration elements, an outlet port for directing a permeate produced by the elements from the vessel and an outlet port for directing a concentrate produced by the elements from the vessel. A number of vessels can be provided in a parallel arrangement and/or a series arrangement and the vessels can be arranged so as to allow regeneration of the microfiltration or ultrationfiltration membranes from another vessel in the arrangement.