A previous study indicated that distilled water could prevent bladder tumor cell implantation in an in vitro assay. We investigated whether a large amount of distilled water irrigation prevented recurrence of superficial bladder cancer in the clinical setting and then we estimated whether cancer cell implantation at the time of transurethral resection is a major mechanism of recurrence. Between May 2000 and January 2002, 22 patients with primary, superficial bladder carcinoma who underwent transurethral resection of bladder tumors (TURBT) were enrolled in this study. The patients underwent bladder washout with 1,000 ml distilled water immediately after TURBT, and then intravesical irrigation with 3,000 ml water for three hours. Control patients were randomly chosen from those who previously underwent TURBT in our hospital and had similar prognostic factors. The 1- and 2-year recurrence-free rates in the patients undergoing distilled water irrigation were both 45% and those in the control patients were 65% and 45%, respectively. There were no significant differences between the two groups. This result indicates that distilled water was ineffective in preventing recurrence of superficial bladder tumor.