Scientists believe that when the Earth initially formed, it was hot and dry, and there was no indoor plumbing. So where did all the water come from?
The current leading theory is that billions of years ago, water was brought to Earth along with impacts by comets or icy asteroids. (Comets are made of rocks and ice.) Archeological evidence suggests that flushable toilets were invented much later, around 1500 B.C., on the island of Crete.
This is pretty amazing, considering that there are 1.37 billion cubic kilometers of water in the oceans. Luckily, we did not have to pay for any of it. At current utility rates, and adjusting for inflation, the water would have cost roughly one third of a million trillion dollars.
Keep this in mind that the next time you're drinking a tall, refreshing glass of "comet juice".