Details (from a leftie perspective) here. Includes information on water as a commodity. And:

The [Plan Puebla Panama] is the most direct threat of corporate water ownership (supported heavily by former President Vincente Fox)...

...Fox wants to transplant the maquiladora, production-for-export model that has been applied with disastrous results in northern Mexico, but with a few new twists. The isthmus is one of the most bio-diverse regions on the planet, and contains some of the most important fresh water reserves in the hemisphere. Exploitation of these resources is key to the plan. "

The US is in support of PPP: "Secretary of State Colin Powell [has] told Vincente Fox that the U.S. will support the plan if Fox militarizes the Mexico-Guatemala border to prevent immigration from Central America northward."