In the first episode of Dear Hank and John they discussed how, when it rains, your own pee could fall on your head! This would occur through evaporation, your pee (or at least the water in the pee) is evaporated into the clouds and then that water falls back down to earth as rain. Now to figure out the probability of this, we need to first determine the amount of pee a human creates in his or her lifetime. According to “science buzz” this is 10,957.5 gallons of pee (41478.6 liters). According to the United States Geological Survey Earth has 332,500,000 cubic miles of water (each cubic mile is over 1.1 trillion gallons). So this means that .000000000000000029958988380041% of earths water is water that was involved in your pee! Now this is a very minuscule amount, however, the average 0.5 gram raindrop contains 9,950,000,000,000,000,000,000 molecules of water! This means that in each drop of rain about 298,000 molecules on average will be from your pee. To put this into perspective an Olympic sized swimming pool (600,000 gallons) filled with a sample of earths water (or rain) would contain about one hundred-millionth of a milligram (one 5-millionth of a drop) of your pee water!