The organ responsible for regulating electrolyte levels in the body is the kidney. Kidneys filter blood, remove waste, and maintain the balance of electrolytes, including sodium, potassium, and calcium. They play a crucial role in homeostasis, ensuring that electrolyte levels remain stable despite variations in diet and hydration. The kidneys work by adjusting the excretion of electrolytes and water based on the body's needs, which is essential for overall health.