The water we drink today could be the same water our ancestors drank, because the earth's water cycle (the hydrologic cycle) continuously recycles our water.

Are We Drinking the Same Water our Ancestors Drank?

Water is continuously mixed and recycled, so the odds favor us sharing at least some molecules of it with Socrates, Jesus, Buddha, or anyone from past eras.

All Matter and Water on Earth is Recycled; So We all Share the Same Water

Here is the logic behind us drinking the same water that our ancestors drank:

  • The earth is a closed system with finite resources; one such resource is water.[1]
  • That means we don’t get new water or lose water on average; instead, it mixes and recycles. The same is somewhat true for air, and most everything else on earth, although each substance has its own considerations.[2]
  • Water is a chemical substance with a chemical formula of H2O, meaning that its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds.
  • People drink an average amount of two quarts of water a day.
  • Each quart of water contains 3.1634653 x 10^24th power of molecules.[3]
  • If a person lives for 75 years, we can calculate them needing roughly 365x75x2=54,750 quarts of water over their lifetime.
  • That means, the average person drinks [very roughly] 54,750 x 3.1634653 x 10^24th power of molecules in their lifetime.
  • There are about 326 million trillion gallons of fresh water on Earth. We have approximately 4.72 X 10^46 molecules of fresh water in total.[4]
  • Thus, there is a fair chance you shared water molecule or two with the Dinosaurs, Jesus, Buddha, Confucius, Julius Caesar, Socrates, or any historical water drinker.

We all share the same water and planet. We always did and we always will. That is why climate change is so critical. Asteroids and sources of water from beyond our planet aside, the water that is here has always been here.

Anything that happened in the water, from the birth of early life forms in oceans to a Dinosaurs taking a pee in a stream, to a corporation dumping toxic waste in our rivers to save money is a story of the same water.

The same thing is true for most other substances on earth, including the combination of molecules we call air. It is possible to share an atom of air with Socrates, but less likely than it is with water. See Breathing Ancient Air.[5]

All the atoms in our bodies and the earth have been around since the start of the universe; we are all made of star stuff.

We only have one earth and one water supply. Our resources are finite.

FUN FACT: That means if you take Communion, there is a slim (but real) chance you are eating and drinking a molecule or two shared between bread and wine and body and blood.

TIP: This article assumes that historical figures like Socrates, Jesus, Buddha, or Lao Tzu, were real people. We could say, Plato, Augustine, or Sima Qian instead. The science is clear, the historical accuracy of any individual’s existence could perhaps be debated. Forgive the clickbait. “Earth is a closed system with finite resources” just didn’t have the same ring to it.

Earth is a Closed System With Finite Resources

The planet Earth is a closed thermodynamic system. That means it does not lose or gain much matter.

Solar radiation comes through our atmosphere. We occasionally get hit by meteors and gain matter, or launch spacecraft and satellites, but the amount of matter in our system remains relatively stable.[6]

All matter and water on earth is recycled so, in absolute terms, the supply remains stable and is repeatedly reused.

Although the absolute amount of water remains stable, it is chemically changed. Plants convert water and carbon dioxide to oxygen and sugars. Respiration reverses the process and makes CO2 and energy. We know that plants take 12,000 billion kg of water a year and that the total amount of water on earth is 1400 billion billion kg. That means that water changes chemically over time.[7]

We are drinking some of the same water as our ancestors, but much is different water on a molecular level. To further complicate matters, Hydrogen atoms move between water molecules, so molecules themselves change over time.

Like coal and oil, water is a finite resource. Fresh water is even more limited. 96.5% of our planet’s water is saltwater, and most of the other 3.5% of our water supply is in the form of ice in glaciers.  Earth’s liquid fresh water is well under 1% of the water supply.[8]

Of all available fresh water on Earth, underground aquifers hold about 30% while lakes and streams hold about 0.3%.[9]

Earth’s Hydrosphere

We know that the planet recycles water using the water cycle. You probably learned about it in school. Water evaporates from oceans, rivers, and lakes; condensation causes clouds; precipitation falls and refills the bodies of water.

For a refresher, see the following video:

Bill Nye the Science Guy: Water Cycle.

Water is part of Earth’s hydrosphere, which includes all water on the planet except water vapor in the atmosphere. Water vapor is the most common greenhouse gas and has tremendous heat-trapping potential and a role in global warming.[10]

The amount of fresh water on Earth remains approximately the same over time, but frequently it is neither available where people can use it nor at the time they need it.

We have droughts, floods, and other catastrophic climate events. 40% of the people on earth live in places where there is a greater demand than supply of water. The percentage of people in water scarce areas is projected to grow to nearly 50% by 2050.[11]

We need to pay attention to our water use and to keeping our finite supply clean.


There is much we don’t know about water. We don’t know whether Earth formed as a dry planet and meteors brought water to it or whether Earth developed water along with other matter as it formed.

For all we don’t know, there is a lot we do know.

We know that the earth’s water cycle (the hydrologic cycle) continuously recycles our water; we know is that earth is a closed system; we know we have finite resources; we know we all breath the same air (roughly speaking) and drink the same water today as we always have.


  1. Our World Is Finite: Is This a Problem?
  2. Why can’t we manufacture water?
  3. How Many Molecules Are in a Glass of Water?
  4. How Many Molecules of Water are on Planet Earth
  5. Breathing Ancient Air
  6. Earth Systems
  7. The Naked Scientists
  8. What Percent of Earth is Water?
  9. Earth’s Freshwater
  10. Water Vapor Confirmed as a Major Player in Climate Change
  11. Fresh Water Watch

"We Drink the Same Water that Socrates, Jesus, and Buddha Drank" is tagged with: Climate Change, Elements, Probability and Odds

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