The effect of water on the catalytic properties of a ruthenium promoted Co/TiO2 catalyst (10 wt.%) 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 4 NL g cat.(-1) h(-1)), the addition of water did not have significant effect on the CO conversion. At lower space velocity (SV = 2 NL g cat.(-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 = I NL g cat.(-1) h(-1)), the addition of water resulted in permanent catalyst deactivation.