water can be lost by breathing, producing faeces and sweating. The kidney works as a filter, generating waste out of the blood which flows to the blader as urine...
what do kidneys filter out???
salt, sugar - (this however is not found in urine), urea, water
concentrated and dilute urine depends on different conditions eg..
external tempurature: high, low
eating salty food
drinking lot of water
All of this is influenced by a hormone called ADH produced in the pituitary gland. The hypothalamus is a part of the brain that controles the release of ADH; it sends messages to the pituitary gland informing if and how much of the hormone should be released. The hormone can now travel in the blood to the kidney where its message is acted upon.