The respiratory system and the urinary system work together to get waste out of the body created from cell respiration. In cell respiration, the 2 waste products are Co2 and water. Water is a substance that the body needs, however you only need a certain amount of water and the body has to get rid of the extras. The respiratory system gets rid of the Co2 in the body by exhaling the Co2 out of the body. The Urinary system takes out the water by draining the water into the kidneys. The kidneys also collect Urea (waste product that is formed from the leftover pieces of broken down proteins), small amounts of calcium, and other salts. Together, the products create urine (95% water and the other 5% urea, calcium and salts). That urine is excreted out of the body and take out all of those products. The respiratory system and urinary system don't actually interact physically, but share the same general functions.
Links to Urinary System-
http://kidney.niddk.nih.gov/kudiseases/pubs/yoururinary/