As Texas lawmakers say farmers in the Rio Grande Valley are hurting because Mexico is not honoring a treaty on surface water delivery, experts caution that greater attention should be paid to water deep below the surface.

Millions of dollars in farm subsidies for irrigation equipment aimed at water conservation have led to more water use, not less, threatening vulnerable aquifers and streams.

A new U.S.

Forty-nine years ago, Ashley Yost’s grandfather sank a well deep into a half-mile square of rich Kansas farmland. He struck an artery of water so prodigious that he could pump 1,600 gallons to the surface every minute. Last year, Mr. Yost was coaxing just 300 gallons from the earth, and pumping up sand in order to do it.

Water, or the lack thereof, is one of the defining challenges of the 21st century. As temperatures rise and droughts become more frequent, the threat of dwindling water resources worries not just environmentalists and governments but companies and their investors, too. Nearly every industrial sector, from food and beverages to mining to pharmaceuticals, depends on water for its operations.

Energy companies are being allowed to pollute drinking water aquifers with oil and gas drilling and fracking waste in Northern Colorado and Denver. Over the past 13 years, the U.S.

A two-day gathering of water experts, farmers and providers this week discussed the need to improve ways of how groundwater is currently managed, which some have blamed for the loss of tens of millions of dollars in economic activity.

Peter Key knew something was strange when the water levels in his tropical fish tank began to go down last summer. Then the washing machine took 40 minutes to fill, and the toilets would not flush. But even as Mr. Key and neighbors spent $14,000 to deepen their community well here, they had identified a likely culprit.

State Engineer Dick Wolfe said Friday that groundwater rules for the San Luis Valley could be ready to submit to court within the next three months.