Interval (missed) cancers and lower than expected mortality reduction of proximal colon cancers in the United States and elsewhere after screening colonoscopy drew attention to quality indicators. Missed adenomas which are more likely to be in the proximal colon may be contributing factors. An independent predictor of the risk of interval cancers is adenoma detection rate. In pilot observations, the investigators showed that water exchange enhanced adenoma detection in the right colon (cecum to hepatic flexure). This prospective, randomized controlled trial will compare water exchange with water immersion and traditional air insufflation in patients undergoing colonoscopy. The investigators test the hypothesis that compared with air insufflation and water immersion, water exchange produces a significantly higher adenoma detection rate in the right colon

All of the procedures will be recorded and stored as digital files.

Inclusion Criteria:

• Patients undergoing colonoscopy performed by the participating endoscopists

Exclusion Criteria:

• obstructive lesions of the colon known before colonoscopy
• massive ascites
• past history of partial colectomy
• refusal to provide written informed consent