Watery Diarrhea – Causes of Wet, Liquid Stool (Bowel Movement)

Normal stool is soft and firm, elongated and passed out with ease. Normal bowel habit refers to passing stool more than 3 times in a week but not more than 3 times in a day. Technically, watery stool is not diarrhea unless it meets with the following criteria to be classified as diarrhea:

  • more than 3 bowel movements in a day
  • total volume exceeding 200 grams or 200 milliliters per day

Althought not strictly defined by the type of stool, many people refer to any watery or loose stool as diarrhea stool.  Usually watery stool occurs with diarrheal illnesses. Read more on diarrhea and normal bowel movement.

Feces should be firm, soft, and elongated like a sausage. This type of “normal” stool is defined in the Bristol Stool Chart as type 3 or type 4 stool. Refer to different types of feces for a graphical representation of the various forms according to the Bristol Stool Chart.

Watery stool (type 7) or mushy stool (type 6) is an indication that the water content in the stool is higher than normal. On average, water should account for approximately 70% of the stool weight, With more fluid stool, the water content to solid matter content is significantly higher than normal.


Why is stool watery?

Food and fluid has to travel from the mouth, down the gut to the bowels and eventually is passed out with stool. Vital nutrients and water are extracted during the course of its transit. Undigested food, water, bile, digestive enzymes, mucus, waste substances and bacteria make up stool. Normally it is firm but soft. However, this more solid form of stool only occurs in the colon.

When the fluid mixture leaves the small intestine and enters the large intestine, water is absorbed to transform the liquid chyme into a solid stool. This happens as it passes through the different parts of the colon, from a liquid form in the ascending colon, to a mush in the transverse colon and finally a firm but soft stool in the descending colon. This reabsorption of water also helps the body preserve fluid.

When there is excessive fluid inflow from the small intestine or when the large intestine is damaged and cannot reabsorb water effectively, then the stool remains watery. These disturbances in the small intestine, large intestine or both are seen with various diseases that are referred to as diarrheal illnesses. It is important to note that diarrhea is only a symptom, and often the predominant symptom, in these conditions.

Dangers of Watery Bowel Movement

The main danger with passing large amounts of watery stool or passing watery diarrhea over a prolonged period is that it results in the loss of vital water and electrolytes. This is known as dehydration which can vary in severity. Mild to moderate diarrhea can be managed with increasing fluid intake, particularly with oral rehydrating solutions.

However, once dehydration is severe or a person cannot rehydrate orally (through the mouth) with even mild to moderate dehydration, then medical intervention is necessary. This often means hospitalization and rehydration through an intravenous drip. Failure to correct dehydration can lead to death.

Causes of Watery Diarrhea

These are some of the more common causes of watery stool, or liquid diarrhea. Also refer to the video below for an explanation of why stool is watery and does not become soft and firm like normal stool.

  • Infections account for most cases of acute watery stool (watery diarrhea). The microorganisms responsible for infectious gastroenteritis are a major cause. Chronic cases of infectious diarrhea may be seen in immunocompromised patients (as seen in HIV diarrhea) or associated with a Clostridium difficile infection (as seen in antibiotic-associated diarrhea).
  • Malabsorption syndromes are another common cause of watery stool or watery diarrhea. In these cases, there is failure of the small intestine to absorb nutrients, which is further compounded by decreased water absorption in the large intestine. The most prominent sign, apart from the watery diarrhea, is fat in the stool (steatorrhea) which gives the stool a greasy appearance and tendency to float (‘floaters’).
  • Chronic intestinal conditions like inflammatory bowel disease (Crohn’s disease, ulcerative colitis) frequently result in watery stool, either as episodes of diarrhea or changes in stool consistency without frequent or large volume evacuations.
  • Functional bowel disorders are group of disturbances where the bowel function is abnormal but not due to any disease. Irritable bowel disorder (IBS) is probably the most well known of these functional bowel disorders. One type of IBS, known as IBS with diarrhea, is marked by abdominal cramps and loose stools, sometimes even watery stools.
  • Food intolerance and allergies where the intestines are unable to process certain foods thereby eliciting symptoms similar to a malabsorption syndrome, the most notable of which is watery diarrhea. This often follows the consumption of the problem foods like dairy in lactose intolerance, gluten in celiac disease or fruits in fructose malabsorption.
  • Poor dietary habits where the diet is full of processed foods, caffeinated drinks, saturated fats and spicy or pungent foods (chilli, hot peppers). This is dependent on individual tolerance and the amount of trigger foods consumed in one sitting. Overeating and dieting or fasting may also trigger watery stool.
  • Medication and toxins either as a result of pharmaceutical drug use, narcotics or poisons which may be intentionally or accidentally consumed. These substances can upset the bowels in various ways thereby causing diarrhea.
  • Psychological factors like stress, anxiety and depression may affect normal bowel movement and result in watery stool or watery diarrhea. It appears that the emotional disturbance may stimulate faster movement through the bowels.
  • Diarrhea due to other disorders may be seen in a number of diseases where the organ, even if not part of the gastrointestinal tract, play crucial roles in bowel functions – digestion and absorption. For example, pancreatitis, gallstones and liver disease. Watery diarrhea may also occur in conditions not linked directly to digestion and absorption of foods as is the case with hyperthyroidism.


Watch this video below on some of the causes of watery stool or read below on all the possible causes.


  1. Diarrhea. NIH.gov
  2. Viral gastroenteritis. Medscape

 Reviewed and updated on 9 August 2018.

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