Rates of adequate bowel preparation in the 60% to 80% range continue to be reported for colonoscopy.To describe the rate of adequate bowel preparation and intraprocedural work needed to achieve this rate in an open-access endoscopy unit. Universal split dosing and regimens tailored to medical predictors of inadequate preparation were used.Prospective observational study.Academic hospital outpatient endoscopy unit and ambulatory surgery center.Outpatients undergoing colonoscopy.Prospective assessment of preparation quality for colonoscopy during insertion and after intraprocedural cleansing in 525 patients.Rates of adequate preparation and work required to improve cleansing quality. Work time for cleaning was measured with a stopwatch.Adequate preparation to allow recommendation of standard screening or surveillance intervals was achieved in 96% of patients, including 6% for whom preparation was adequate only after intraprocedural cleansing work. The mean time for intraprocedural cleaning was 4.1 minutes and constituted 17% of total procedure time. Work time for cleaning and fluid volume injected increased when worse preparation grades were identified before cleaning.Single-center study with low percentage (4%) of patients receiving Medicaid.An open-access unit using split-dose bowel cleansing preparations can achieve high rates of adequate bowel preparation for colonoscopy. Intraprocedural cleansing accounts for a substantial fraction of the total procedure time in colonoscopy and is an important contributor to high rates of adequate preparation.