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A World of Water A recent issue of National Geographic contained an article entitled “Water Pressure” which dealt with water as a limited resource on Earth. The idea of water being limited seems hard to fathom for many of us. What follows is a conversation that I had with myself on the subject: I’ve seen satellite photos of the Earth, the majority
of the photo is blue with water. So how can there be any shortage? That’s a lot of H2O! So what is the problem? A full 97% of that water is found in the oceans. This water is too saline to be used for drinking, irrigation, or even industry. Desalinization is currently too expensive to be a large scale answer to any water shortages we may face. Hold on! I just did the math. According to your numbers, we have close to 10 million cubic miles of fresh (non-salt) water on the planet. I still don’t see how water can be limiting. Well, out of all of the fresh water on the Earth, over two-thirds is locked up in glaciers and ice caps. When you get down to it, less than one percent of the water on Earth is both fresh and available to use. Okay, so we only have 3.26 million cubic miles of usable fresh water. I guess you’re going to tell me that we are using it up too fast and soon there will be none left. That isn’t quite how it works. You see we don’t really use water up as much as recycle it. Recycle water? Yes. Haven’t you ever heard of the water cycle? It is the process in which water moves around, through and above the Earth. There is constantly water or water vapor moving all around us. Even in a drought? The water cycle is a global phenomenon. It may be dry here, but its raining somewhere else. In fact, about 4 trillion gallons of water falls to Earth each day. Most of the 3,100 cubic miles of water in the atmosphere is in the form of vapor. When it falls back to Earth its in the form of rain, snow and ice. So what happens once it hits Earth? Generally there are two paths for the water to go. One is to move across the surface, the other is for it to soak into the ground. If the water stays on the surface it will flow until it reaches a lake or the ocean, that is if it doesn’t evaporate before it reaches its final destination. If water soaks into the ground it can end up stored there for quite a while, but at some time it will make its way back to the surface. You mean like through a spring? Yes, ground water will make its way to the surface through things such as springs, artesian wells and seepages. Ground water can also be pulled up to the surface by humans and through the roots of plants. Okay, so how does it get back into the atmosphere? I’ve already mentioned evaporation. Water that is on the surfaces will evaporate into the atmosphere. This can be water in a puddle, a pond, a river and the ocean. Approximately 2.5 trillion gallons a day re-enter the atmosphere by way of evaporation. A second way water vapor moves into the atmosphere is through transpiration. Transper-what? Transpiration. Plants are constantly pulling water up through their roots and then passing the water out through the leaves where it enters the atmosphere. This process is known as transpiration. If the amount of water remains the same on Earth, how can it be a limiting resource? While the total amount of fresh water remains relatively constant across the Earth, the demand doesn’t. The global population grows by 219,000 people everyday. All of these people require fresh water. If demand continues to grow we can only expect more shortages of water in the future. It should also be noted that the distribution of water is not even across the globe. Sometimes water is a limited resource because there is not enough of it in a region. The southwest United States is a great example. How so? The Colorado River was once mighty enough to carve out the Grand Canyon.
It now reaches the ocean as a mere trickle because the water is diverted
to quench the thirst of the arid southwest. The Colorado River is a water source for about 250 million people. Another big drain on the river is irrigation. In fact, 70% of the water used globally goes into growing food. That’s a lot of people drinking Colorado River water. Yes it is. In the U.S. we rely on surface waters (rivers and lakes) for about 80% of our water, with the rest coming from underground. Of course there are some regions where one or the other is the whole source of water. I guess we should look at things from a global perspective since the water cycle is such a large scale phenomenon. What is the global outlook? The United Nations predicts that 2.7 billion people will face a water shortage by the year 2025. Along with water shortages, we have to be concerned with the purity of our water. There are 1.2 billion people in the world that don’t have clean drinking water, something we in the United States sometimes take for granted. Not only is it important to be aware of our water use, and misuse, it is also important to protect what we have. The amount of fresh, clean, accessible water is finite. We need to do everything we can to protect it. Dan Obrecht
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