Excerpted from Water in Plain Sight: Hope For A Thirsty World by Judith D. Schwartz, with permission from St. Martin’s Press. Copyright 2016.

When it comes to irrigation, water is not simply water.

This is dogma to John Kempf, an Ohio farmer who has made a career of improving crop health and agriculture yields. In 2006, Kempf founded the company Advancing Eco Agriculture, a consulting service for farmers that provides testing and analysis of crop specimens and recommends various plant nutrition treatments to improve crop yields.

The sources of water used for crops—be it well, river or reservoir—vary as to the mineral salts that they carry. The degree to which salts are present in water is referred to as “hardness,” generally described in terms of grains per gallon. (“Salt” in this context is not what you’d sprinkle on scrambled eggs, but the combination of elements with a positive charge [cation] and negative charge [anion].) Kempf says that poor water quality, specifically water with high levels of calcium carbonate (lime), is a problem not often acknowledged in public discussions of agriculture—but one that affects crop production and, ironically, leads to a higher use of water.

“The level of minerals affects not only plants’ ability to absorb water, but also how the plant can absorb nutrition,” says Kempf. “Hard water requires more energy, and therefore nutrition, to break it down. When water quality is poor, more water is required.” Farms do regularly test for water quality, and he says that when a potential client’s water source has more than five grains per gallon he recommends that it be treated.

“When farms irrigate with poor-quality water there are multiple effects,” he says. “It ties up all the nutrients that have been applied in the form of fertilizers. It significantly suppresses soil biology. And what often happens is that sodium and calcium bicarbonates accumulate in the soil profile. This leads to salinity.”

By binding nutrients and inhibiting biological processes in the soil, hard water undermines the plants’ ability to reach higher stages of health. This results in less-resilient crops and precludes the water-saving efficiencies that characterize robust plants. Plus, additional water may be needed to correct the problems associated with poor-quality water. For example, soil salinity is typically addressed by flushing the area with large amounts of water. That’s why salinity tends to be a problem in dryer areas like Australia and the northern Great Plains in Canada and the United States. In Vermont, for example, copious rains easily wash out excess saltiness. However, Kempf is not talking only about places like California, where he says the situation is endemic. “Ohio, Pennsylvania and the entire Midwest have this problem,” he says. “But no one talks about it.”