Which organ's main function is to eliminate excess water and waste products from the body?

The kidney's primary role in the body is to eliminate excess water and waste products through the process of urine formation. This organ is essential for maintaining homeostasis, regulating electrolytes, and filtering blood to remove toxins and metabolic waste. The kidneys filter approximately 50 gallons of blood daily, reabsorbing needed substances while allowing waste products to be concentrated and eliminated.

The liver, while crucial for detoxification and metabolizing nutrients, primarily functions in processing substances rather than excreting them from the body. The stomach's main purpose is digesting food rather than waste elimination. The intestine is involved in absorbing nutrients and water, with waste elimination being a secondary function through feces formation. Thus, the kidney is the organ specifically specialized for the excretion of excess water and waste products, making it the correct answer.