Water Can Be Too Pure

Jack W. Dini, Livermore, CA

(This appeared in Hawaii Reporter, January 24, 2007)

Can water be too pure? If you’re a farmer the answer is yes. Desalinated water is one example. The purity drawback is that desalination not only separates the undesirable salts from the water, but also removes ions that are essential to plant growth. When desalinized water is used to replace irrigation water, basic nutrients like calcium, magnesium, and sulfate at levels sufficient to preclude additional fertilization of these elements is missing.

An example is a new facility in Ashkelon, on Israel’s southern Mediterranean coast. Although the Ashkelon facility was designed to provide water for human consumption, because of relatively modest population densities in southern Israel, a substantial percentage of the desalinated water was delivered to farmers. Recent evaluation of the effect of the plant’s desalinized water on agriculture, however, produced some surprising, negative results. Water from the Ashkelon plant has no magnesium, whereas typical Israel water has 20 to 20 mg/liter of magnesium. After farmers used the desalinated water, magnesium deficiency symptoms appeared in crops, including tomatoes, basil, and flowers, and had to be remedied by fertilization. To meet agricultural needs, missing nutrients might be added to desalinized water in the form of fertilizers, adding additional costs. If the minerals required for agriculture are not added at the desalination plant, farmers will need sophisticated independent control systems in order to cope with the variable water quality. (1)

Farmers can also be affected by run-off water that is too pure. Snow-melt run-off from the Sierra Nevada, Cascades, or other mountains can be too pure. For irrigation to be effective it needs to penetrate into the soil supplying enough water to sustain the crops until the next irrigation and the most important factor for water penetration is salts (or lack thereof) present in the water and/or soil. A lack of calcium in the majority of soils due to snow-melt irrigation water, or poor quality subsurface water, is leading to serious problems in California. Danyal Kasapligil, agronomist in Fresno, CA, reports, “What we are seeing in the field is, not only are there more and more water penetration problems, but crop quality is also rapidly declining because of a lack of calcium in our irrigation water.” (2) Brent Rouppet adds that for irrigation water to penetrate deeply into the soil, the electrical conductivity of the water needs to be greater than approximately 0.60 dS/m (decisiemens per meter). Irrigation water with less than 0.60 dS/m conductivity contributes to loss of soil structure and increased water penetration problems. The snow-melt run-off from the Sierra Nevada Mountains is so pure that its electrical conductivity can be 0.02 dS/m, or less. This water lacks calcium, essential for good soil structure, and any calcium existing in the soil profile is over time leached below the root zone or used by the crops and is typically not being replaced in quantities required. (2)

Here’s another example where absolute purity of water can be a problem. Philip West of Louisiana State University notes, “With productive waters, it is quite apparent that absolute purity is out of the question. If the Mississippi River passing Baton Rouge and New Orleans consisted of distilled water there would be no seafood industry such as we now have in Louisiana. With copper ‘contaminating’ the water there would be no oysters. Traces of iron, manganese, cobalt, copper, and zinc are essential for the crabs, snapper, flounder, shrimp and other creatures that abound in Gulf waters. As unpleasant as it sounds, even the run-off from the fertilized fields of the heartland’s and the sewage discharges into the Missouri, Ohio, and Mississippi River systems pollute and thus ultimately nourish the waters.” (3)

One last item. Are you a bottled water fan? If so, you could be giving up a primary source of fluoride which is the public health system’s main weapon against tooth decay. What comes in the bottle has either been filtered to remove impurities or is spring water that is reputed to purer than tap water. But the filtering process also takes out fluoride. Not only does fluoride occur naturally in water, but about half the nation’s public water supplies are supplemented with additional fluoride. The recommended level of fluoride set by the EPA for municipal water systems is 0.7 to 1.2 parts per million (ppm). The maximum acceptable level is 4 ppm. If a water supply contains less than 0.7 ppm of fluoride, dentists recommend the use of a fluoride supplement, in tablets or liquid, from birth unto the later teen-age years. (4)

When researchers in Ohio sampled more than 50 brands of bottled water for fluoride content, they found that 90 percent of them had levels below the recommended range for dental health. (5) In South Australia, a study found a 71 percent rise in tooth decay in children which was attributed to the lack of enamel strengthening fluoride in the bottled water that has become so popular in the area. (6)

References

1. U. Yermiyahu et al., “Rethinking Desalinated Water Quality and Agriculture,” Science, 318, 920, November 9, 2007
2.Brent Rouppet, “Irrigation Water: A Correlation to Soil Structure and Crop Quality?” Crops, August 2006, Page 22
3.Raphael G. Kazmann, in Rational Readings on Environmental Concerns, Jay H. Lehr, Editor, (New York, Van Nostrand Reinhold, 1992), 311
4.Marian Burros, “Eating Well; Bottled Water: Is It Too Pure?” nytimes.com, November 22, 1989
5.“Fluoride Alert,” Runner’s World, 35, 32, July 2000
6. Verity Edwards, “Bottled water a dental disaster,” Australiannews.com, August 2, 2006