Methods on the day of exam. Enrolled patients will be sent to the endoscopy room and colonoscopy will be performed by the principle investigator. Patient lie on the left lateral position with right hip and knee flexed and left leg straight. When the PI about to start the single-handed colonoscopy examination, the blinded observer open the sealed envelops with the code enclosed. A standard colonoscope will be inserted. Patient may be ordered to change the position and or abdominal compression may be applied by nurse to aid the colonoscope advancement. Oximetry, cardiac rhythm and blood pressure will be monitored during examination. Blinding will not be performed in this study because of the feeling of water or air effect inside the colon can be differentiated by the patient so that in our opinion it actually can not be blinded..The control method includes usual air insufflation during insertion and shortening maneuvers. The study method includes only water infusion (air pump is turned off) through the colonoscope during insertion since the scope is inserted into the anus until reach the cecum. Water will be infused as needed under endoscopist judgement through the adaptor on biopsy channel with endoscopic washer pump. The usual air insufflation will be used during colonoscope withdrawal to facilitate mucosal examination and perform any other intervention, such as biopsy. Hypothesis testing: The unsedated colonoscopy with natural temperature water infusion minimize the pain symptoms than unsedated colonoscopy with usual air insufflation.