In a prospective, randomized, controlled study, two methods (water method vs. air method) of performing colonoscopy will be compared in patients undergoing unsedated colonoscopy for CRC screening. The investigators hypothesize that:

1. Study method increases overall cecal intubation with comparable assessment of current experience and patient willingness to repeat future colonoscopy compared with conventional colonoscopy
2. Study method improves bowel preparation and increases polyp pickup rate

Colorectal cancer (CRC) screening for the high and the low risk healthy asymptomatic Veterans Affairs (VA) patients is being promoted. Compliance with this Directive will result in an increased number of VA patients undergoing colonoscopy.

The demand for colonoscopy far exceeds the capacity available to perform the procedure in the VA system. The conventional practice for colonoscopy at VA facilities across the country is to perform colonoscopy under conscious sedation with air insufflation. Efficiency is governed by the fact that sedated patients require time and space for recovery and these are major limiting factors in the current setting for the use of colonoscopy for CRC screening.

In a prospective, randomized, controlled trial (RCT), two methods of performing colonoscopy will be compared in patients undergoing unsedated colonoscopy for CRC screening. We compared the water infusion in lieu of air insufflation (water method) with the conventional air insufflation method. We hypothesize that the water method (Study method) increases overall cecal intubation with comparable assessment of current experience and patient willingness to repeat future colonoscopy compared with conventional colonoscopy. In addition, the water method improves bowel preparation and increases polyp pickup rate.

Inclusion Criteria:

• Adult (>50 years old)
• Male and female patients
• Scheduled and consented for screening or surveillance colonoscopy without medications
• Accept randomization to the study or the conventional method
• Agree to complete study questionnaires
• The adults will be normal healthy patients or patients with mild systemic disease, ASA 1 or ASA 2.

Exclusion Criteria:

• Patients who decline to participate
• Unable to give informed consent or complete the questionnaires due to language or other difficulties