This study is concerned with the effect of water quality and pH adjustment in the pretreatment of feed water on nanofiltration (NF) membrane fouling. The results show that water with higher alkalinity and calcium concentration is prone to foul NF membranes through the deposition of calcium carbonate. However, fouling caused by this kind of water is also more likely to be effectively controlled by dropping the pH value of the feed water using the addition of acid. Further, in this study, hydrochloric acid was found to be a better acid agent than sulfuric acid, as the former induced much lower flux decline rate as compared to the latter. This probably is due to the generally lower solubility of sulfate salts as compared to that of chloride salts.