How Long Before a Colonoscopy Should I Stop Drinking Water?

How Long Before a Colonoscopy Should I Stop Drinking Water?

Usually, doctors recommend patients undergoing a colonoscopy to stop drinking clear liquid or water at least three to four hours before the procedure. However, patients with diabetes and who are dehydrated may take a few sips of water after consulting their doctor. On the day of the procedure, patients may take only those medications as discussed previously with their physician (laxatives and blood pressure, heart and seizure medications) with a sip of water. For a successful colonoscopy, the bowel must be cleaned well. This will enable the doctor to clearly see the lining of the bowel. Poor preparation may mean that the procedure will have to be stopped, and patients will have to repeat the procedure on another day.

What is a colonoscopy?

A colonoscopy is a test to look at the inside of the colon. The test will help find problems such as growths (polyps), tumors, redness (inflammation) and areas of bleeding. Doctors may also perform surgical procedures such as polyp removal during a colonoscopy. Patients will be given medicines to help them relax (a sedative) before and during a colonoscopy.

  • A colonoscope is a long, slender, flexible tube about the thickness of a finger that has a camera at the tip, enabling doctors to examine the entire colon.
  • Doctors insert it into the body through the anus and gently guide it through the rectum and colon. They administer sedatives to patients during the exam to keep them comfortable and relaxed. They usually perform the test in the hospital as an outpatient procedure.
  • The colonoscope provides doctors with magnified images of the inner wall of the colon and rectum. If the doctor finds a polyp during the examination, they can pass instruments through the colonoscope to remove polyps or tissue samples.
  • The lab will check the extracted tissue samples for the presence of cancer cells.
  • Some patients may be eligible for a virtual colonoscopy, which uses advanced computed tomography (CT) technology and computer software to produce images of the colon.
  • Nursing staff will care for patients until they are awake and comfortable (30 to 60 minutes). Some patients may experience mild bloating and stomach cramps, which are normal.
  • Once the anesthesia wears off, doctors may allow patients to leave the hospital along with discharge diet and instructions. Patients should not drink alcoholic beverages for 24 hours after the procedure. They can resume usual activities the next day.

What are the possible risks of colonoscopy procedures?

Colonoscopy is a standard medical procedure, but all such procedures have some risks. These problems do not happen often.

  • Rarely, the instrument may tear the wall of the colon. This may require surgery.
  • There may be adverse drug reactions or heart/breathing complications.
  • In rare instances, bleeding may occur, usually when tissue or polyps are removed. This may mean being admitted to the hospital for additional care, which may require a transfusion or surgery.

What are the other types of methods available for screening colon cancer?

Apart from a colonoscopy, doctors may also recommend the procedures below to check for any unwanted growths in the colon.


  • A sigmoidoscope is a slender, flexible tube about the thickness of a finger that has a camera at the tip.
  • Doctors insert a sigmoidoscope into the lower part of the colon through the rectum.
  • The sigmoidoscope provides doctors with a view of the inner wall of the rectum and lower colon, allowing them to search for polyps or cancerous tissue.
  • The tube is about two feet long, so doctors can examine half of the colon. The test is performed in the physician’s office and can be uncomfortable but is generally not painful.


  • Using an ultrasound probe inserted into the anus, sound waves mark an array of points that are converted to an image seen on a video monitor.
  • Viewing the pictures allows doctors to see the integrity of the sphincter muscles (muscles of the anus).
  • An ultrasound is also used in the rectum to measure the depth of growth of tumors.

Imaging exams

  • If screening exams suggest the presence of cancer, advanced imaging techniques such as ultrasound, magnetic resonance imaging (MRI), positron emission tomography (PET) and computed tomography (CT) scans are used to determine if cancer has spread to other organs and tissues.

Double-contrast barium enema

  • Prior to taking an X-ray, doctors fill the colon with air and a white, chalky liquid called barium.
  • Barium and air show an outline of the colon, rectum and any polyps or abnormal tissue on the X-ray.


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Medically Reviewed on 5/17/2021


Medscape Medical Reference

Harvard Medical School

National Cancer Institute