All Water Cycle Diagrams are Wrong

by Michael J. McGuire

One or more times during everyone’s grade school science class experience, we were introduced to the water (or hydrologic) cycle.  The water cycle continues to be taught today the same way I remember learning it far too many years ago.  Water in its various forms is shown moving throughout our world.   Water is neither created nor destroyed just transformed and moved around.  So far, I am in agreement.  However, water moving from oceans to clouds to rain to fresh water lakes and rivers is then described as being the source of drinking water for the planet.  Unfortunately and with very few exceptions, the water cycles that we grew up with are dead wrong.  The consequences of them being wrong are not academic.  These incorrect water cycles have shaped how all of us understand where we get our drinking water.  It comes from rain, right?  Wrong.

One website put the problem in clear text:  “Run and get a glass of water and put it on the table next to you.  Take a good long look at the water.  Now — can you guess how old it is?  The water in your glass may have fallen from the sky as rain just last week, but the water itself has been around pretty much as long as the earth has!”

Despite its shortcomings, Wikipedia is used by a lot of people including students as a source of information on many topics.  The Wikipedia Water Cycle article (accessed August 7, 2012) repeats the misconception that water just cycles through the earth and sky.  “By transferring water from one reservoir [ocean, soil, river] to another, the water cycle purifies water…”  On the Wikipedia Water Cycle page is a representation of the water cycle provided by the U.S. Geological Survey, which is certainly an authoritative source.   However, this depiction while more detailed and sophisticated than the one above is still wrong as an illustration showing from where our drinking water comes.

Even the U.S. Environmental Protection Agency website shows a water cycle diagram that is wrong.  “The water you get from your faucet can come from two places – from the water in lakes or rivers (surface water), or from water that comes from wells (groundwater).”  There are some words on the web page that describe the need to purify drinking water before it can be used but the impression left by the diagram is a lot more powerful than the words.

I could show thousands of examples of incorrect water cycle diagrams.  A Google search of “water cycle” returned 3,520,000 results in 0.25 seconds.

A related problem exists with diagrams showing water pollution.  The pollution cycle shown on the Merriam-Webster website illustrates the misconceptions.  Shown are the sources of pollution, but not the solutions to pollution, namely wastewater treatment facilities and, more importantly, water treatment facilities that take out the contaminants before water is distributed to consumers.

What is lacking in the depiction of water and pollution cycles is a fundamental explanation of how water that moves through the hydrologic cycle is contaminated with chemical and biological pollutants and then cleansed through water treatment processes to make it safe for all of us to consume.  The consequence of decades of misinformation about where our drinking water comes from is that the public truly does not understand that a good part of our drinking water comes from sewage.  When attempts are made to exhaustively treat wastewater and use it as part of an indirect potable supply, the public and the media rise up in outrage.  No “toilet-to-tap” in our town!

Water professionals know that all water came from someone’s toilet at some point.  Drinking water from underground sources, rivers, lakes, reservoirs and even desalinated seawater spent some part of its long history as sewage.  A brilliant article by Charles Fishman writing for National Geographic stated clearly that even “…Evian water was pee at some point.” David Jenkins, now Emeritus Professor at UC Berkeley, always gave his new students a problem figuring out how many molecules of Cleopatra’s pee were in a glass water.  Avogadro’s number tells us that Cleopatra put out a lot of molecules!

Fishman’s article made the point that we do not mind using silverware in a restaurant that was in someone’s mouth a few hours before.  Nor do we mind using a towel in a hotel that someone had used a day or so previously.  Obviously, we do not mind reusing forks and towels because we know that they have been properly cleaned.  Indeed, our drinking water is also properly cleaned even if it was sewage at some point.

In Fishman’s article he refers to a February 9, 2012 New York Times article by Felicity Barringer who made the argument that the “Yuck Factor” is not as big a problem as it once was for wastewater reuse projects.  Barringer identifies an environmental group that acknowledged that all of our water is reused at some point.  One volunteer noted “It isn’t toilet to tap.  It’s toilet to treatment to treatment to treatment to tap.”  I could not agree more, but I am pretty sure that not everyone is so enlightened.

We have to overcome a significant barrier before wastewater reuse will be widely accepted:  decades of telling people that their water comes from pure rain that falls from the sky right into their glass.  We have to change how the water cycle is taught in our schools and described by the media.  In an earlier blog, I showcased a short film made by Sahana Singh called “The Forgotten Cycle” that won TU Delft’s Urban Water Movie Contest.  It shows that not only do contaminants enter water as it moves through the cycle but it also shows that there are treatment technologies available to purify the water before it is consumed.  Ms. Singh is on the right track.  Surely, there are clever people in the world who can tell the water cycle story correctly.  Our ability to fully reuse wastewater as an important part of our potable water supply depends on all of us making the effort.

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About safedrinkingwaterdotcom

McGuire is an environmental engineer and writer. He has worked in the drinking water community for over 40 yrs
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4 Responses to All Water Cycle Diagrams are Wrong

  1. Well said, and I think pee is the least of our worries. People put things like paint thinner, gasoline, medications etc, down the drain all the time with little thought as to how this may affect the water.

  2. Wendy Wilson says:

    So what is the correct diagram? In the watershed protection world we often use the Water-Energy cycle diagram from U.S DOE which at least explains a few things.

  3. Wendy–An excellent question. See my latest post The “Drinking Water Cycle” is Right

  4. Pingback: 2012 in review | safedrinkingwaterdotcom

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