The spiral wound membranes operate on the next principle: After the pretreatment, raw water is being brought to the membrane housings containing semi-permeable spiral wound membrane elements by booster pump. Raw water is than passed through the membrane layers. In this step of the filtration, unwonted substances are being removed from the water creating waste water called – concentrate (retentate). Remaining part of the water presents clean water and it is called – permeate. Depending of the type of the membrane filtration wide range of unwonted substances can be removed from the raw water.