Desalinated Water: Great to Drink, Bad for Crops

Nov. 8, 2007 -- Dreams of someday watering crops with desalinated water have hit a small snag.

Farmers using drinking-quality water from the world's largest desalination plant in Ashkelon, on Israel's southern Mediterranean coast, have discovered that the water is lacking in some needed elements, like calcium and magnesium, and too rich in boron.

That's not a problem for humans drinking the water, but it's terrible for tomatoes, basil, citrus trees, flowers and other economically important plants. Fortunately, with some adjustments and fertilizers, the water can be made usable for farmers, now that the problem is recognized.

"The conventional wisdom was that desalination is an incredible bonus for farmers," said Alon Tal, of Ben-Gurion University's Negev Sede Boger Campus in Israel.

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The bonus would be that desalinated water helps reduce the salts in soils. In theory the excess salts found in the soils of many hot, dry parts of the world could be made less salty with desalinated water. And since few food plants are especially salt tolerant, that would be a bonus for growers fighting salty ground.

The newfound drawbacks of desalinated water only came to light because until recently desalinated water was too expensive to use on crops. It's the scale and high efficiency of the Ashkelon plant, however, that lowered the cost of the water to where it became attractive to Israeli farmers.

"The desalinated water was not planned or anticipated to ever be supplied to farmers for irrigation -- it was always promoted as being for domestic/municipal consumption," explained Alon Ben-Gal and Uri Yermiyahu, who are coauthors with Tal on a paper about the findings in the Nov. 9 issue of the journal Science.