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Newsletter and Technical Publications

Lakes and Reservoirs vol. 2

The Watershed: Water from the Mountains into the Sea

What This Booklet Is All About

Adequate supplies of fresh water are the single most important natural resource for human well-being, survival and socioeconomic development. It is no accident that early human settlements developed near rivers, lakes and other freshwater sources. Fresh water also is a fundamental feature of the global landscape. Indeed, as seen from space, the Earth largely appears as a globe with an expansive blue mass of water (Photo 1). From the perspective of human water needs, however, this picture is very misleading. Most of this water resides in the world ’s oceans and is too salty for human use. Or else it is locked up in glaciers and ice caps, or situated deep under the land surface, essentially beyond easy human reach.

Why is fresh water so important for human existence? The most obvious answer is that humans are composed largely of water. Without adequate supplies of clean, safe fresh water, we would all die within a relatively short time. The plants and animals we eat as food also require water. Further, our socioeconomic development depends on adequate supplies of this natural resource. We use fresh water for a myriad of purposes, including growing food and livestock, cleaning, cooking, industry, commercial and sports fisheries, aquaculture, recreation, aesthetics, hydro-power production and transport of commercial goods. It is no surprise, therefore, that areas with scarce supplies of fresh water typically have limited socioeconomic development.

Photo 1: Earth from Space; a blue planet.

In view of its importance to human existence, water has been characterized by some as precious, finite and irreplaceable. This description is certainly valid. It is precious in that we need it to satisfy our physiological needs and to fuel economic growth. It is finite in that our planet only has a fixed quantity of it. It is irreplaceable in that we have no substitutes for it. Unfortunately, it is also very sensitive to human activities, and can easily become over- exploited and/or polluted because of such activities.

It is the intention of this publication to follow water from the time it falls on the land surface as precipitation, through the various water systems and water-bodies it encounters on its overland journey back to the oceans, and the myriad of hydrologic and physical components that can affect it on its journey. This booklet also provides a description of the overall cycle of water on the planet Earth, as well as an indication of the availability and characteristics of our global water resources.

Table of Contents

• Brochure
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• International Year of Forests
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• World Environment Day
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• UNEP Campaign
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