BACKGROUND: The water method facilitates colonoscope insertion in unsedated patients. OBJECTIVE: To compare quality indicators in sedated veterans. DESIGN: Performance improvement. SETTING: VA endoscopy unit. PATIENTS: 368 consecutive screening patients. INTERVENTION: Air or water method assignment (high definition colonoscope) was based on the last digit of social security number. MEASUREMENTS: Adenoma detection rate (ADR), cecal intubation rate; intubation and withdrawal times; sedation requirements and external pressure used. RESULTS: ADR was higher with the water method (57.1% vs. 46.1%, p=0.04). After controlling for age, body mass index, smoking, alcohol, withdrawal time and quality of bowel preparation, the odds of detecting an adenoma was 81% higher with the water method (OR 1.81; 95% cI: 1.12-2.90). In the proximal colon ADR was higher with the water method (45.8% vs. 34.6%, p=0.03), including adenomas <10 mm in size (41.8% vs. 31.4%, p=0.04). The water method showed significantly longer cecal intubation time (6.9±0.3 vs. 5.3±0.3 min, p=0.0001); less external pressure used (11.9% vs. 28.3%, p=0.0001); lower need for additional sedation (17.5% vs. 27.2%, p<0.03). LIMITATIONS: Predominance of males, single unblinded endoscopist with high ADR. CONCLUSIONS: The water method is an independent factor associated with significantly higher ADR. Replication by blinded colonoscopist(s) is indicated.