Not long ago, I was talking with a friend of mine about The Longest Straw, and he raised an interesting question: why should we worry about water conservation when water is an infinitely renewable resource?  After all, even when we waste water by flushing it down our sewer systems or pollute it, doesn’t that water just evaporate and re-enter the natural water cycle anyway?  So why does it matter? It wasn’t a bad question, so I figured this post is as good as any to tackle that question, and explain how even a renewable resource can be consumed at a rate beyond its ability to replenish.

First, even though 75% of the earth’s surface is covered in water, only 2.5% of the earth’s water is drinkable.  The rest is either salty (desalination is not developed to the point to be feasible on a massive scale), polluted, or frozen in the ice caps.  And of course, when rain water falls, not all of it is claimed- so the rain that falls in the ocean, or in polluted water sources, ends up unusable.  This is a major problem in Los Angeles, where the majority of our runoff ends up in the Pacific Ocean.

The other concern is that the water cycle is, for lack of a better term, slow.  “Residence time” is the amount of time water remains in one state before moving on to the next stage of the water cycle, and this handy chart (about halfway down the page) looks at the average residence time for various kinds of naturally occurring water.  The water in our atmosphere will remain about 9 days before condensing then falling as rain.  Groundwater won’t evaporate for 300 years.  Water in the ocean will remain there 3,100 years, and glaciers will remain in their frozen state 16,000 years.

In other words, yes, we can waste water and pollute our lakes, and that water will, in time, naturally recycle itself through the water cycle.  However, generally speaking, we won’t see that water in a clean, drinkable state again until long after our grandchildren’s grandchildren have passed away.

Finally, almost 800 million people in the world today have no access to clean drinking water.  If you’re reading this blog post from the US or elsewhere in the developed world, consider yourself very lucky.  While there’s not much we can do in our own communities that will impact the drinking water needs of, say, rural China, we can conserve here to protect our own communities.  As the population continues to grow and threatens to exceed the capacity of our existing water infrastructure (a threat that Los Angeles has faced on multiple occasions over the past century), we might come to realize that our current standard of living is simply not feasible.  Even as a renewable resource, drinking water is just too scarce, and the water cycle is too slow, to accommodate billions of people who treat this precious resource as disposable.

Just remember the TLS motto: “Without water, there is no life.”