Mild dehydration can cause symptoms such as weakness, dizziness and fatigue. Severe dehydration can be life-threatening. Too little water intake can cause elderly people to appear demented, when they are not. A lack of fluid in the body can cause decreased blood supply to the brain; that causes confusion. It can cause improper distribution of electrolytes throughout the body. Electrolyte abnormalities cause many problems. Fluid loss can cause kidney failure, coma, shock, etc. Make sure mom and dad drink lots of water!