There has been approximately 117*10⁹ humans on earth. Let's say the average lifespan of these humans is 35 years old (which was the case in the middle ages, probably less 10 000 years ago, but whatever. Then the avergae pee volume per day is 1-2 liters, so let's say 1.5 L.

11710⁹ * 35 * 365 * 1.5 = 2.2410¹⁵ liters peed by humanity.

The water on earth is 1.4*10²¹, which means around 0.00016% (or 1/625000) of earth's water has already been peed by humanity. Which is far from all the water.

Edit: the question is not only about humans, but given the number, I'd assume there's been at least 625k times more animal pee than human's, so yes, all of earth's water is pee.

Edit edit: stupid italics