Dehydration is the lack of water in the body. This occurs when water loss is greater than intake.
A healthy adult, about 7 liters of water from digestive juices is secreted into the intestine and about 2 liters of dietary water is ingested every day, but only 100-200 ml of water is lost with the stool, since most of it is re-absorbed in intestine.
When the Dehydration is Critical:
If 20 liters of water (and electrolytes) are lost in one day, it would be an acute diarrhea, which needs immediate attention and shifting of patient to a hospital or health care centre.