Kidney stones appear when a substance is excreted through the urine in bigger concentrations than urine can dissolve it. Sufficiently large substances that can’t be dissolved by the urine precipitate in the renal pelvis and transform into stones. Additionally, metabolic disorders can complicate matters and cause higher production of such substances in larger quantities. When these substances are excreted through the urine in larger concentrations, they can increase the risk of precipitation. Some physical conditions also decrease the ability of urine to dissolve excreted substances... even if those substances are excreted in smaller concentrations. This is the reason doctors encourage patients with kidney stones to drink liquids (water) as often as possible. Expelled stones are then examined to identify their chemical ingredients. According to their chemical nature, a proper diet is then recommended to decrease the likelihood that similar chemical substances enter the body again, and repeat the process.