In the past, membrane filtration was considered to be a rather futuristic, expensive and complicated process, applicable only in arid regions and for industrial separation problems. However, in the past decade the process appears to have developed into a mature, reliable unit operation that merits serious consideration, also in the field of water supply in the Netherlands. The quality improvement achieved by the process is outstanding; almost all possible contaminants are removed virtually completely (with the exception of low molecular weight and/or apolar organics). The cost of membrane filtration has decreased significantly lately as a result of developments in design and new membranes. The process is still more expensive than conventional processes, i.e. NLG 0.80 - NLG 1.00 per m3 treated water. However, in a number of cases, it is possible to treat only a part of the total flow in order to obtain the desired reduction in salt content. By applying split-treatment e.g. a 50% reduction in parameters like hardness, Na, Cl, NO3, SO4 and the like can be obtained at a cost of NLG 0.40 - NLG 0,50 per m3 drinking water. Recently, two applications of membrane filtration in the field of water supply in the Netherlands have been investigated, i.e. : 1. Reduction of the salinity (Na and Cl) of the drinking water of the Westland Water Company (WDM). 2. Reduction of hardness and salinity (Na and Cl) of the drinking water of PS Andijk of the Provincial Water Board of North Holland (PWN). In both cases it was concluded that applications of membrane filtration in a split treatment process was feasible and realistic, while the costs are not unacceptable, i.e. NLG 0.40 - NLG 0.50 m3 drinking water. Discharge of the brine does not cause major problems, because the brine consists only of 5 times concentrated drinking water. Based on these results the conclusion seems justified that membrane filtration today is a realistic option in the field of water supply in the Netherlands. When the increasing pollution of raw water sources which leads to increasing concentrations of NO3, SO4, Cl, Ca, Mg, Na, K is kept in mind it is apparent that more applications of membrane filtration will be considered in future.
