This study was carried out to evaluate the performance of nano-filtration (NF) and reverse osmosis (RO) technology for reducing the total salt concentration from waste water. The nano-filtration proved very effective in removing the polyvalent cations and anions, such as SO4 -, whereas the removal efficiency was 97.22 %. It is well known that a RO water-treatment process removes all the cations and anions from waste water or brine or sea water, especially removing the monovalent ions such as Cl -where the removal efficiency was 94.4 %. The performance efficiency of RO and NF water-treatment processes declined significantly during the first 3 years of operation due to fouling and biofouling of the membrane. The research findings provided a concrete clue for the important issue of water treatment as an alternative to existing water use methods on a cost-effective basis. The research also highlighted the potential to replace the NF and RO membranes used in these two water-treatment techniques. Keywords: desalination of waste water, reverse osmosis, nano-filtration Izvedena je bila {tudija ocene zmogljivosti tehnologije nanofiltracije (angl. NF) in povratne osmoze (angl. RO) za zmanj{anje skupne vsebnosti soli v odpadni vodi. Nanofiltracija je zelo u~inkovita pri odpravljanju polivalentnih kationov in anionov, kot so SO4 -, kjer je bila u~inkovitost odstranitve 97,22 %. Dobro je poznano, da RO postopek obdelave vode odstrani vse katione in anione iz odpadne vode, slanice ali morske vode, {e posebno monovalentni Cl -, kjer je bila u~inkovitost odstranitve 94,4 %. Zmogljivost RO in NF procesov pri obdelavi vode se ob~utno zmanj{a med prvim 3-letnim obratovanjem zaradi ma{enja in biolo{kega nalaganja na membrane. Ugotovitve raziskave omogo~ajo konkreten namig za pomembno vpra{anje obdelave vode, kot cenovno u~inkovita alternativa sedanjim metodam. Raziskava je pokazala tudi mo`nost za zamenjavo NF in RO membran, ki se jih uporablja v teh dveh na~inih obdelave vode.