This randomized controlled trial aims to evaluate the effects of different ratios of electrolyte beverage and water combined with polyethylene glycol (PEG) on bowel preparation quality before colonoscopy. Participants undergoing elective colonoscopy will be randomly assigned to one of three bowel preparation regimens: PEG prepared with water only, PEG prepared with a low ratio of electrolyte beverage and water, or PEG prepared with a medium ratio of electrolyte beverage and water. The primary outcome is adequate bowel preparation assessed by the Boston Bowel Preparation Scale (BBPS). Secondary outcomes include bowel preparation completion rate, tolerability, adverse events, repeat colonoscopy rate, adenoma detection rate, and ingestion rhythm characteristics during bowel preparation. This study also aims to explore whether electrolyte beverage-assisted bowel preparation may improve bowel cleansing quality by influencing participants' ingestion rhythm and adherence during PEG intake.

Inclusion Criteria:

• Adults aged 18-75 years scheduled to undergo elective colonoscopy
• Meet the standard clinical indications for colonoscopy;
• Able to understand and comply with the bowel preparation procedure and complete oral polyethylene glycol (PEG) intake as required;
• Able to comply with study-related data collection and follow-up;
• Provide written informed consent voluntarily.

Exclusion Criteria:

• Previously diagnosed colorectal cancer, intestinal obstruction, or suspected intestinal obstruction;
• Active gastrointestinal bleeding or a definite history of gastrointestinal bleeding within the past 4 weeks (including melena, hematochezia, or hematemesis);
• Severe renal insufficiency, decompensated heart failure, significant electrolyte imbalance, or other conditions unsuitable for PEG bowel preparation;
• Known allergy to polyethylene glycol or components of the electrolyte beverage used in the study;
• Pregnant or breastfeeding women;
• Any other condition considered by the investigators to make the participant unsuitable for the study.