To evaporate, sweat absorbs a lot of energy: about 580 kilocalories per liter, drawn from your skin. During intense exercise in hot weather, you can sweat more than a liter an hour. But sweat that drips off without evaporating barely cools you at all. That's why humid heat is so draining.
Every day, your kidneys filter around 180 liters of blood plasma, about a bathtub's worth. Yet you only have about 3 liters of plasma, so it passes through your kidneys some sixty times a day. Over 99% of the filtered water is reabsorbed, leaving just one to two liters of urine.
A 70 kg adult is made of about 7 × 10²⁷ atoms, or seven billion billion billion. The observable universe is thought to hold on the order of 10²² to 10²⁴ stars. Even with the high estimate, you contain thousands of times more atoms than there are stars in the entire visible cosmos.