Studies concerning the removal of natural organic matter (NOM) from surface and tap water by nanofiltration are presented. The separation and transport characteristics of nanofiltration membranes were determined. The degree of NOM coefficient and water hardness removal from surface water and a reduction of water hardness were studied. The content of organic matter, both in the feed and the permeate, was estimated by the determination of total organic carbon (TOC), colour, turbidity, chemical oxygen demand (CODMn) and the absorbance in ultraviolet at a wavelength of 254 nm. The investigations demonstrated the complete removal of humic acids determined as the UV254 absorbance, and a high removal of colour (93.3%), TOC (93.5%) and turbidity (85.5%).