The seven states that share Colorado River water have agreed on a plan to deal with drought issues and future water shortages.
However, a dispute over whether Arizona and Nevada can tap in-state tributaries remains unresolved.
Nevada has nearly exhausted its Colorado River apportionment and wants to draw water from the Virgin River, a tributary of the Colorado. States on the upper river object to the plan.
But to avoid a showdown on that issue, the states pledged to work on finding alternative sources of water that could replace the Virgin River supply.
Those alternatives would have to be in place by 2012, when Nevada says it will run out of existing resources.
If the dispute lands in court, it will drag Arizona with it, jeopardizing as much as half of the water that flows to Phoenix and Tucson through the Central Arizona Project canal.
The upper river states have also raised questions about Arizona's use of tributaries, in-state rivers that, like the Virgin, flow into the Colorado.