Can 7 liters of water per day be harmful for any organ within a human body?

Yes: Are you thirsty, or is this a habit/lifestyle? Diabetes or Kidney or Pituitary Gland diseases can cause thirst, and urination. A good rule is 1-2 ounces water flood for every 1 pound of body weight. Excess water intake such as you describe can lead to severe lowering of your body's Sodium level, and can cause cerebral swelling, and seizures and severe consequences.