Did you know that March 22 is World Water Day? The United Nations page explains that this year, the focus is upon shared water. There are 263 transboundary lakes and river basins that cover 145 countries and constitute 1/2 of the earth's surface. We don't just share water on the surface - about 15% of the world's aquifers are represented in 274 transboundary aquifers.
A couple of interesting statistics from the United Nations. A person needs to drink 2-4 liters of water a day. But it takes 2000 to 5000 liters of water to produce one day's supply of food. 1000-3000 liters of water are required to grow 1 kilo of rice and 13000 to 15000 liters of water to produce one kilo of grain-fed beef. Now consider that the earth's 6 billion population is already using 54% of all the accessible freshwater from rivers, lakes and aquifers. Mmm. What happens when the world's population increases?
About 1% of all the water on the planet is accessible freshwater. Roughly 97% is saltwater and 2% is trapped in the snowpacks. (I know what you are thinking - let's don't and say we did.)
Drink up: taking the salt out of seawater describes the technology used for desalination of seawater for coastal cities. In the Middle East, where oil is abundant, distillation - heating the water to form steam is popular, but it costs almost $1 per cubic meter of water. For oil-importing nations, desalination is more economical. Reverse Osmosis can produce water for $0.68 to $0.90 per cubic meter of water.
Perhaps many of you remember a high school science experiment where you placed a membrane bag of saline solution inside a flask of freshwater. Remember how the fresh water transferred through the membrane in an attempt to equalize the salinity and the bag puffed up to almost burst? (See Experiment of the Week for another version of the osmosis experiment that does not require a membrane bag.)
Reverse osmosis causes water to flow through the membrane in the opposite direction - from high salinity to low salinity. However, it takes energy - up to 1200 pounds per square inch of pressure to force the water to flow through the membrane.
The Tampa Bay Seawater Desalination plant produces up to 25 million gallons per day day drinking water. It is currently America's larges seawater desalination plant. Those membranes enabling reverse osmosis are fragile - sand and diatomaceous earth filters are necessary to to eliminate all sediment and other microscopic particles before the salty water is pressed through the membranes. A membrane pore is about 1/100,000th the diameter of a human hair, or 0.001 microns.
A couple of weeks ago, I wrote, What is Happening to the Dead Sea? It is becoming deader, if can speak Ozark-ian for a moment. The reason is not global warming, but overuse of the resource, resulting in ever-increasing salinity levels. As I remarked, eventually it will become so salty that it will not evaporate. I am concerned about the indiscriminate construction of desalination plants across the globe. We need to think about it.
Years ago, I read that someone proposed generating power by bringing seawater (via pipe or canal) to the Dead Sea. The difference in elevation could potentially generate large amounts of electrical power. Wonder what ever happened to that idea? I'm not sure what effect it might have on the Dead Sea, but it's already much saltier than the ocean, so I don't think it would be contribute to making in any "deader".
Posted by: The Navigator | March 23, 2009 at 06:17 PM