Two things we know about Arizona: One, we need affordable electricity to survive and prosper in the Arizona desert; and two, we have limited water resources. Today we will begin looking at this complicated relationship by assessing how much water we use to generate electricity in our State.

I want to highlight for you some important concepts on this point. First, Professor Martin Pasqualetti of Arizona State University has looked at “The Water Costs of Electricity in Arizona” for the Arizona Water Institute, Arizona Water Institute Study

Professor Pasqualetti determined how many gallons it takes to produce a megawatt hour of electricity in Arizona for the following types of generation:

• Nuclear power consumes 785 gallons/MWh
• Coal consumes 510 gallons/MWh
• Natural gas consumes 415 gallons/MWh

Professor Pasqualetti then calculated the five-year average generation numbers for Arizona, and came up with these figures:

• Nuclear power generates 27,492,437 MWh

• Coal generates 38,526,671 MWh

• Natural gas generates 30,135,321 MWh

Multiplying the gallons/MWh and MWh generated yields the following totals:


• Nuclear
  • 785 gals/MWh * 27,492,437 MWh =1,954,650,000 gals

• Coal
  • 510 gals/MWh * 38,526,671 MWh =1,773,780,000 gals

• Natural gas
  • 415 gals/MWh * 30,135,321 MWh =1,058,665,000 gals


Total water consumed to generate electricity is thus 53,736,323,470 gallons.

In America, large gallonages are measured in ‘acre-feet’, the number of gallons needed to cover an acre of land in one foot of water; which is 325,851 gallons.

So Arizona uses 53,736,323,470 gallons, which is divided by 325,851 to yield 164,910 acre-feet of water to generate electricity.

An acre-foot is assumed to provide enough water for 2 households and the portion of the community’s needs (such as their share for parks, and school grounds) attributable to those homes.

In Arizona, nuclear, gas and coal-fired electricity generation use as much water as 329,820 homes. 

But we’ve left out one major electricity generator - hydroelectric power.  Professor Pasqualetti looked closely at this issue because it can get tricky.

Reservoirs serve several purposes, they produce electricity through hydropower, they hold water for irrigation, domestic water uses, and they benefit tourism and recreation by providing boating, fishing, and camping amenities.

All told, he found that Arizona’s hydropower reservoirs evaporate about 56,000 gallons for each MWh, but when factoring for the non-hydropower benefits, the gallonage drops to 30,078 gallons/MWh.

This is where the numbers get big, and controversial.

Hydropower producers point out that Colorado River dams were built to store and provide water to farms and communities - hydropower is a side benefit.  So along the Colorado, when water flows through the dam it does so to provide water for farms and communities. 

Unfortunately, that view leaves out the fact that hydropower is frequently used to meet spikes in demand.  Hydropower is available nearly instantly so it can be dispatched at a moment's notice to meet a surge in demand or a sudden drop in supply (e.g., a plant goes offline suddenly).  

The only thing certain is that hydropower must have some effect on water supplies, because when water flows solely for peaking demand and not as a water supply action, evaporation increases.

In future posts, we will explore the energy-water nexus as it moves from electric generation to electricity use for transporting water. As always, we encourage your feedback.