A presentation by a radical architect to an elite Manhattan crowd last night highlighted a ferocious business problem. There’s not enough water for California and Mexico (or many other pairs of over- and under-fed economies) to share.

Teddy Cruz, whose practice focuses on the informal urban life around the San Diego- Tijuana border, was addressing the Van Alen Institute about how we should construe and outfit national borders. Van Alen  is now in its 106th year of airing how design can promote social equity and healthy cities. (I’ve talked to Van Alen about possible collaborations but have never worked for the organization.) Its purpose includes a drive to harmonize architectural  practice with progressive policy. In our cultural moment, when the  federal government has created a setaside for high design, I expected the forum to talk about lighting and GIS. But Cruz played up something starker.

Asked by his co-panelist to explain how concerns about human rights at the border can influence the politics of environmental regulation, Cruz described how the water on one side of the line he knows best looks limpid and serene. The other side, he said, looks like something between tin and dirt. And I leave you to guess which is which.

This is a center of immigration, remittances, trade and creativity for North America. And, as Cruz explained, “the future of this area depends on the politics of water.”

The business of allocating, treating and bidding water will be just as ugly, and just as vital, as anything else in the changing economy.