Effects of feed water concentration, temperature, pressure and flow rate on membrane performance are examined using a reverse osmosis (RO) system with a product capacity of about 5 m(3)/d. Performance characteristics of Hollow Fibre and Spiral Wound permeators, connected in parallel to the feed water system, are also evaluated. Experiments were conducted using salt (NaCl) solution of known concentration. Flow rates and concentrations of product and reject waters were closely monitored during the experiments. Product recovery is found to increase with feed water temperature and pressure, but decrease with increasing feed water concentration and now rate. Salt passage increases with feed water temperature and concentration, but decreases with increasing feed water pressure and flow rate. Although hollow fibre and spiral wound permeators have different physical configurations, both react similarly, though with slightly different degrees, to the changes in experimental conditions. Notably different is their respective product recovery and salt passage, which can be qualified by the different morphological characteristics of the two membranes. Under identical feed conditions, product recovery of hollow fibre varies from 12%-30% while that of spiral wound varies from 6%-18%. Degradation analysis is inconclusive since it is likely that membrane operation has not stabilized after only 100 h of operation.