Sharon B. Megdal is director of the Water Resources Research Center at the University of Arizona and is a professor in the Department of Agricultural and Resource Economics. She is also a professor and specialist in the Department of Soil, Water, and Environmental Science. She is director of the University of Arizona Water Sustainability Program. She has a doctorate in economics from Princeton University.

Other articles by Sharon B. Megdal:

Some ideas on water Don't negate agricultural water use

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Paragon Electric
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Prestige maintenance USA
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Wentz and Patrick Construction
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Q Do you think it's good government here when we the people are told to accept, pay to clean up and use second-rate Colorado River water while ground water is used for agriculture?

A Good government depends on one's vantage point and I think the person posing this question has formulated his/her answer.

Millions of people use Colorado River water. The laws and system of water rights authorize agriculture in the Active Management Areas to utilize groundwater for land that was irrigated during the 1975 through 1979 period. I think it is unlikely to envision a scenario that takes these rights away. Urban growth has reduced the number of acres in production in the Tucson Active Management Area.

Q What set of assumptions go into projections of future water supply? I've seen an estimate that we have enough water to support a million more people. Does this estimate assume we will receive our full allocation of Central Arizona Project (CAP) water? If so, is that estimate realistic in view of a recent study projecting lakes Mead and Powell have a 50-50 chance of going dry by 2021?

A Projections clearly depend on assumptions. The study I did in 2006, "Water Resource Availability for the Tucson Metropolitan Area," clearly lists every assumption and includes scenario analysis. Changing the assumptions will change the answer regarding how many people water supplies available to the region can serve.

My study did not include use of any Indian Central Arizona Project water by non-Indian water users. Two Indian Nations have subcontracts for CAP water. The municipalities and Indian Nations will receive their full allocations under some shortage scenarios.

Regarding the recent study mentioned by the questioner, there, too, assumptions matter. At the Water Resources Research Center Annual Conference, to be held on June 24 in Phoenix, some speakers will address issues related to shortages on the Colorado River and efforts to incorporate climate change in the modeling of Colorado River flows.

Q What is the current wisdom regarding the 30- to 50-year sustainability of available water resources in the Tucson area? How dependent is Tucson on the continued availability of Central Arizona Project water?

A I am not sure what is meant by 30- to 50-year sustainability of available water resources. There are sufficient supplies for current residents and water providers. Developers are still able to show 100-year assured water supplies, many times through membership in the Central Arizona Groundwater Replenishment District (CAGRD).

It is true that Tucson Water, for example, shows that it needs some additional resources several years out if it grows at the projected rate and other assumptions are correct. There are supplies available to the Tucson region, such as 14,000 acre-feet of CAP water in the control of the State Land Department.

This water is not included in Tucson Water's plans, nor the plans of any other water provider. That's one example of the uncertainties of water planning for the region. It is the case that the Tucson region's ability to meet the requirements of the Assured Water Supply Rules depends on utilization of CAP water.

Q What is the scientific credibility for developers' assurances made to prospective homebuyers who ask that a 100-year water supply be guaranteed before the development could go forward?

A In addition to other information, if groundwater is to be used, hydrological studies must be submitted to and reviewed by the Arizona Department of Water Resources prior to issuance of an Assured Water Supply designation or certificate. Call the Tucson office at 770-3800 for more information about this.

Q If we are not running out of water for people, how will the mines affect water supply?

A Except for water conservation regulations in the Active Management Areas, the mining industry has the ability to drill wells and use groundwater for mineral extraction.

The study I did in July 2006 on water resources available to the Tucson region used information from the Arizona Department of Water Resources to quantify how much the municipal sector would rely on "mined" groundwater, meaning groundwater that is not replenished.

This assumption reflects the provisions of the Assured Water Supply Rules, which pertain to the municipal sector only. The vast stores of groundwater in our region are part of our drought "insurance."

Any increases in groundwater pumping by the mines will affect our progress toward meeting the water management goal of safe yield.

Higher overdraft of our aquifer will mean reductions in our insurance. The extent of groundwater level declines and other implications of increased pumping would depend on the amount of groundwater pumping that occurs and if there is any replenishment of the groundwater used.

For additional information, check out the "Layperson's Guide to Arizona Water," which can be downloaded at no charge from www.cals.arizona.edu/azwater.

Other publications and reports are also available at that site, as well as links to other water sites.