Has the Water From Your Faucet Been Inside a Dinosaur? Science Says Yes — But With Caveats

Yes, the water flowing from your tap has likely passed through the bodies of prehistoric creatures like dinosaurs or mammoths, according to a back-of-the-envelope calculation by Neil Donahue, director of the Steinbrenner Institute for Environmental Education and Research at Carnegie Mellon University. However, experts caution that this conclusion depends on assumptions and that not all water on Earth has cycled through living organisms.

How Long Would It Take to Pee the Ocean?

Donahue’s estimate hinges on the average human producing about 1 liter of urine daily, with all animals peeing roughly 1% of their body weight. If all 2.2 billion tons of chordates (a group including mammals, birds, and fish) excreted water at this rate, it would equate to 0.2 gigatonnes of urine per day, he calculated. Dividing Earth’s total water—1.4 billion gigatons—by this daily amount suggests it would take 7 billion days, or roughly 19 million years, to “pee out the whole ocean.” Since dinosaurs went extinct 66 million years ago, Donahue argues that mammals alone have likely peed more than an ocean’s worth of water since their rise.

“Even mammals have probably peed more than an ocean since we took over,” Donahue said in an email to Live Science.

What About Water That’s Never Been in the Cycle?

David Kreamer, a hydrology professor at the University of Nevada, Las Vegas, agrees that ancient pee has likely cycled through the water system but disputes the idea that every drop of water has been excreted. He points to “juvenile water,” a term for water trapped deep in Earth’s crust that has never surfaced in the planet’s history. This water, released during volcanic eruptions, could enter the cycle for the first time, he explained.

“There’s some deep groundwater that’s been underground for tens of thousands of years,” Kreamer said. “And juvenile water hasn’t really emerged from the depths of the Earth ever in Earth’s history.”

Why the Water Cycle Isn’t Perfectly Efficient

The water cycle is not a continuous process. Water can remain locked in glacial ice for hundreds of thousands of years or reside in underground aquifers for millennia. These delays mean some water has not yet cycled through animals, including humans, Kreamer noted.

“Water doesn’t move through the cycle at a constant speed,” he said. “Some water hasn’t been in the cycle, and that’s a key point.”

FAQ: Key Questions About Water’s Journey Through Time

• How much water does a person pee daily? The average person produces about 1 liter (0.26 gallons) of urine per day, according to Donahue’s calculation.
• What is juvenile water? Juvenile water is trapped deep underground and has never entered the water cycle. It is released through volcanic activity, according to the U.S. Geological Survey (USGS).
• How long does water stay in the cycle? Water can remain in glaciers or aquifers for thousands to millions of years, slowing its return to the surface.

The debate underscores the complexity of Earth’s water systems. While Donahue’s math suggests ancient pee is likely in today’s water, Kreamer’s insights highlight that some water remains untouched by life’s cycles—proving that even the most basic elements of our planet hold mysteries.

For further reading, the USGS provides detailed data on global water distribution here.