Water is of vital importance in the desert southwest. Simultaneously, efforts to reduce greenhouse gasses (GHGs) are causing solar power plants to spring up, like flowers after the desert rains, and they are bringing their water demands with them. This conflict, over water, is and will stress limited resources even farther.
At its roots, there are four main contenders for water in the region: humans, aquifers and the natural environment, nature (animals, fish, etc), and energy. Energy production takes vasts amount of water. A modern gas-fired power plant can consume as much as 15 gallons a minute. How does a solar plant consume water? Washing. In order to maintain optimal efficiency the panels must be washed free of dirt and dust, usually daily, sometimes more often. This can use 1000s of gallons a day, in an already arid region.
In states like California, Arizona, and Nevada, competing demands take their toll. For example, in California, reducing water draw from the Sacramento delta has become a battle between Northern California, the smelt, Southern California, inland farmers, and the Federal Government. Currently the issue stands in favor of the smelt and the Federal Government, but I am sure competing interests will manage to stake their claim in some fashion or another. Issues like this have caused solar development in California to increasingly rely on low-water solar facilities. Similar fights are being waged in parts of Nevada between towns and solar developers.
What this means is that a careful analysis of the trade-offs are between agriculture, energy, and human water consumption must be. Solar energy is vital in reducing emissions from anthropocentric (human-related) climate change. At the same time individuals must still eat, shower, drink, and partake of all the other activities we take for granted.
I am certain that in time solar facilities will require less and less water. But until that time, the trade offs inherent in its use, as well as with large-scale agro in the desert, must be weighed and balanced to make sure that we are making the correct long-term decisions.