The effect of water on the catalytic properties of a ruthenium promoted Co/TiO 2 catalyst (10wt.%) during Fischer-Tropsch synthesis (FTS) was investigated in a continuously stirred tank reactor (CSTR) by adding water into the feed gas at varying space velocity. At higher synthesis gas (syngas) space velocities (SV=8 or 4NLgcat. - 1 h - 1 ), the addition of water did not have significant effect on the CO conversion. At lower space velocity (SV=2NLgcat. - 1 h - 1 ), the addition of water decreased the CO conversion; however, the decrease was reversible with the catalyst quickly recovering the activity that it exhibited prior to water addition. At high CO conversion (space velocity of SV=1NLgcat. - 1 h - 1 ), the addition of water resulted in permanent catalyst deactivation.