Mar 04 2019Share

What Impact Does Precipitation Have On Our Drought and Water Supplies?

By Warren Tenney

When you live in a place where drought spans multiple decades, every bit of precipitation receives an enthusiastic welcome, but what does that really mean to our drought status, and what effect does it truly have on our water supplies?

The most recent winter storm brought essential moisture to areas across the State providing a short-term relief to our environment including our vegetation, which reduces the risk of catastrophic wildfires. The precipitation increases the amount of water in local reservoirs which improves their overall status. In addition, rain and snow in the Upper Colorado River Basin results in more water flowing into Lake Mead reducing the likelihood of Colorado River supply cutbacks.

However, when we take a step back and get a look at the big picture, this winter’s rain and snow are merely a few drops in a very large bucket and cannot erase multiple dry years. Research shows that drought cycles and wet cycles in Arizona can run 20 to 30 years, and the current record-breaking drought cycle began around 1999. The last eight years have also been the driest on record in the Salt and Verde rivers’ watersheds. So realistically and historically, it would take a few years of greater than average snow and rain to begin to heal the wounds left by the current drought.

The AMWUA cities understand this historical cycle and the basic fact that we live in the desert so they have built with drought in mind. The cities have made significant investments to prepare their infrastructure and build a diverse portfolio of water supplies so they can ensure the delivery of this essential resource to their residents and businesses. But what is a water portfolio and why does that matter?

By having more than one supply of water, the cities are prepared for both long-term and short-term challenges. In other words, they do not rely on one bucket to fill everyone’s glasses. This diversity increases our security. Let’s take a look.

Salt River Project (SRP)

•    SRP delivers water captured behind dams on the Salt and Verde Rivers, supplemented by groundwater, through 131 miles of canals to the AMWUA cities.

•    AMWUA cities use SRP supplies to meet 41 percent of their collective demand.

•    Recent research shows the SRP water supply to be very resilient to the worst known droughts, even in the tree ring record, as well as climate change forecasts.

Want to learn more about Salt River Project? HERE is a great place to begin.

Central Arizona Project (CAP)

•    The 336-mile-long canal brings water from the Colorado River into the Phoenix and Tucson areas.
•    AMWUA cities use CAP supplies to meet 45 percent of their collective demand.

•    Cities have a higher priority when it comes to CAP deliveries and will not be the first cut when Colorado River supplies are reduced.

Want to learn more about the Central Arizona Project? You’ll find the answers on their WEBSITE.


•    The AMWUA cities understand the importance of preserving groundwater and have been stalwart supporters of the 1980 Groundwater Management Act.

•    The AMWUA cities rely on naturally occurring groundwater for only five percent of their needs.

•    The aquifers that contain groundwater beneath our feet are vital to our way of life. They supply a portion of the water we use, and they act as underground reservoirs to buffer if water deliveries from SRP or CAP are reduced.

•    With little precipitation, these aquifers naturally replenish very slowly.  Much of the water in the aquifer is “fossil water,” trapped underground eons ago. It is not a renewable supply.  Therefore, we must carefully manage these aquifers.

•    There is a significant amount of naturally occurring groundwater beneath our feet. This water is the ultimate back-up if other sources fail. However, this groundwater is not a renewable resource and should not be relied on as a long-term supply.

Learn more about groundwater HERE.

•    AMWUA cities use effluent, or recycled water, to meet nine percent of their collective demand.

•    Effluent is a drought proof, renewable supply that is available whenever we use water.

•    AMWUA cities collectively put over 90% of their effluent to beneficial use, but not all of it is used within their service territories. For example, five AMWUA members deliver effluent to the Palo Verde Nuclear Generating Station for cooling purposes.
A diverse portfolio of water supplies increases reliability and that is vital to residents and businesses, to our way of life, and our overall economy. AMWUA cities are fortunate to have access to water from the SRP system and Colorado River water delivered by CAP.  AMWUA cities have built a unique, complex, and robust infrastructure network to utilize all these supplies and ensure water is always available. The extreme unpredictability of water supplies in the desert requires a higher level of planning and preparedness. This means AMWUA cities’ water supplies are arguably more secure than those of cities in significantly wetter areas. And this is why we can support such a large population in the desert.

In the end, precipitation in our arid climate is always welcome, but the reality is it will take more than a few memorable storms to have an overall effect on our long-standing drought.  At least in the meantime, we are built for drought.

For 50 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit

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