Budgeting Water Properly
3 Pages Posted: 31 Aug 2020
A primary requirement for managing water effectively and sustainably is an accounting framework that registers the water that is available for use (supply) and the water that is being used (demand). A common accounting analogy is a water budget, or a water account. This note focuses on the water budgets of individual countries, defining concepts including renewable water, watershed, water withdrawal, water consumption, and dependency ratio. The note also includes data on the water budgets of Myanmar and Egypt.
Dec. 16, 2019
Budgeting Water Properly
A primary requirement for managing water effectively and sustainably is an accounting framework that registers the water that is available for use (supply) and the water that is being used (demand). A common accounting analogy is a water budget, or a water account, from which water can be drawn down (or not).
Discussions of global water resources often focus on the stock of water, meaning how much water is available in oceans, glaciers, rivers, and so on, at a given moment in time. It is then argued that on a global scale, total freshwater use is but a fraction of the total available fresh water, and that there is little reason to worry about water scarcity because water is a renewable resource that is constantly replenished through the global water cycle. Studies of the global water stock are very useful, but to understand water stress, it may be more important to focus on water flows and to take a more local perspective. On a less-than-global scale, water may be less renewable.
The flows of water are continuously replenished, and thus are available on a sustainable basis during a particular period of time, say a year. The concept of renewable water captures exactly that notion. The most natural unit to think of in a water budget is probably the watershed: an area of land that captures water and drains into a lake, stream, or river via streams or ditches, directly over the surface or through the ground. Precipitation, in the form of rain and snow, deposits water in the watershed, and then the water finds its way to the river. Agriculture, industry, and cities along the river withdraw water from it. For downstream users, it is critical to know what fraction of the water that upstream users withdraw is returned to the river. In the case of power plants, for example, a very high fraction of the water withdrawn will be returned, whereas in the case of agriculture (and in particular agriculture with, say, drip irrigation), only a small fraction of the withdrawn water is returned.
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Keywords: water budget, renewable water, watershed, water withdrawal, water consumption, dependency ratio, Myanmar, Egypt, ecology, world economy
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