Question: what are the side effects from not drinking enough water?
Answer: Persistent headaches. One of the first things you might notice when you're dehydrated is a throbbing headache. ... 
Sluggish bowel function. “There are water receptors in the colon, and they pull water from the body to make the stools softer,” says Dr. ... 
Dull skin. ... 
Fatigue. ... 
Weight gain. ... 
Dry mouth.