2.79B understand that urine contains water, urea and ion

 Urine: produced by kidneys after needed substances are re-absorbed into blood

Component	Explanation
Water	excess water that is not re-absorbed at collecting duct (depending on ADH levels) will be a component in urine
Salts	excess salts not filtered by Loop of Henle (depending on body water concentration) will be a component in urine
Urea	high levels of urea is toxic so will always be removed from the body in urine