This is an excellent article on dehydration. Link
Some highlights:
- Fluid is lost through urination, sweating, breathing, and defecation.
- The kidneys regulate fluid balance, causing the body to conserve fluid when needed or excrete it when not needed.
- Severe dehydration can cause low blood pressure.
- The body’s cells do not work correctly when dehydrated (especially the brain).
- Dehydration can occur from vomiting, diarrhea, sweating, and using diuretics.
- Children and the elderly are especially susceptible.
above link = https://labtestsonline.org/conditions/dehydration