We’ve got a fascinating border water fight going on between Mexico and irrigators in the United States over water from the Rio Grande right now. But rather than the usual issue – who gets how much – this one’s over when the water is used.

Under US-Mexico treaty, Mexican irrigators are entitled to a set amount of water, to be delivered at their head gate on the US-Mexico border. Until it’s needed, the water is stored upstream in Elephant Butte Reservoir, on the Rio Grande in southern New Mexico, as part of a pool of water for use by southern New Mexico and Texas farmers.

This drought-short year, Mexico called for a delivery of water beginning April 1, while the Texas and New Mexico farmers were planning on waiting until later in the summer to begin their irrigation season.

As a result, in order to get Mexico’s water all the way to their border head gate, a substantially larger release was required, as the AP’s Christopher Sherman explains:

It’s more efficient to move a lot of water than a little, especially when the riverbed has been a sandy sponge for months. Irrigation districts estimate twice as much water will be lost to seepage than delivered to Mexico in this release, and those losses come out of the U.S. share, not Mexico’s.

As I wrote last week:

Wet years have a way of covering up a multitude of water management sins. Drought exposes them for all to see.