The performance of a forward osmosis (FO) system may be characterised by the assessment parameters: FO-RO flux ratio (J(w)/J(w(RO))), apparent FO water permeability (J(w)/(pi(ds) - pi(ml))), and the newly developed flux efficiency factor (J(w, ob)/J(w, re)). The former two parameters offer information on extent of internal concentration polarisation and driving force utilisation, respectively. The J(w, ob)/J(w, re) factor has practical relevance, and reveals the inevitable trade-off between flux and recovery (phi) for a FO system. The derived J(w, ob)/J(w, re) factors corresponded well to experimental observations. High water permeability, low salt-to-water permeability ratio, and large mass transfer coefficient improve the performance of a FO system, but these may also be influenced by operational and fouling effects, such as draw solute transmission, fouling resistance and cake-enhanced concentration polarisation. It was shown that membrane properties also play a significant role in fouling behaviour. Fouling amelioration factors include aeration and osmotic backwash. A thin-film composite membrane showed potential for FO application with favourable intrinsic transport parameters. It was demonstrated that a FO system could achieve stable water production with both relatively high flux efficiency (J(w, ob)/J(w, re) = 0.8) and high recovery (phi = 95.8%), which attested to the technology potential. (C) 2012 Elsevier B.V. All rights reserved.