Eden found that his urine appears yellowish on a hot day. Explain how the kidneys regulate the water balance in her body on hot day.

The kidneys maintain our body's water balance by controlling the water concentration of blood plasma. The kidneys also control salt levels and the excretion of urea. The main job of your kidneys is to regulate the amount of water in the body and balance the concentration of mineral ions in the blood. Whatever isn't used is secreted.