Why might having an excretory system that excretes urine be a disadvantage in a desert environment? how can desert animals overcome this disadvantage?

In a desert, water is in scarce supply, so excreting water would be a bad thing and might cause the death of any animal that does so due to dehydration. There can be several different mechanisms to overcome this. One would be to have the bladder discharge urine into the large intestine where the water can then be reabsorbed into the body while the urea in the urine is passed out along with other solid wastes produced by digestion. Some other methods of conserving water would be for the kidneys to extract more water from the urine leaving the urine fairly concentrated. Also animals may behave in manners that conserve water such as staying in the shade during the day and only being active at night.