The body keeps its internal conditions steady using negative feedback. When it is hot or during hard exercise, we sweat. Sweat cools the body as it evaporates, but it also removes water and salts, so the blood becomes more concentrated. This is dehydration if the water is not replaced.
The brain detects the more concentrated blood. It causes thirst, so the person drinks, and the pituitary gland releases more ADH. The collecting ducts become more permeable, more water is reabsorbed, and the kidneys make a small volume of concentrated urine. Sports drinks aim to replace the water and salts lost in sweat.
Excess water intake has the opposite effect. The blood becomes diluted, less ADH is released, less water is reabsorbed and a large volume of dilute urine is made, which removes the extra water.
After a high salt intake, the blood becomes more concentrated. Thirst increases and more ADH is released, so water is saved while the kidneys remove the extra salt in a small volume of concentrated urine. In every case, the response returns the blood to its normal concentration.