How does the Kidney Reduce the Water Content of Urine on a Hot Day? Blog Intro: For most people, a hot day is an enjoyable experience. But for those who suffer from renal disease, it can be life threatening. When the body becomes overheated a series of reactions occur to help cool down: sweating, increased heart rate and blood circulation, vasodilation and an increase in urine production. The kidneys are able to reduce the water content of urine produced on a hot day by using an enzyme called 'renalase.' Renalase works by breaking down urea into ammonia and carbon dioxide, which are two products that evaporate more easily than liquid water.