Where does Tucson get its water?

Hi all.  As I was riding my bike to school avoiding all the puddles, I was thinking about where the water we drink in Tucson comes from.  If you think about it, we don’t have any flowing rivers (for all of you not from Tucson, we have “washes,” which are dry river beds that flood every so often during a large rain event – image to the right), but when we turn on our taps, water flows out.  So where do we get our water?

Rillito River, Tucson, AZ. Courtesy of http://www.tucsonazrealestateblog.com/tucson-real-estate/.

Historically, Tucson has pumped water from the regional aquifer (sediments below the surface that are saturated with water – like a sponge); while our population was small, this was a renewable source of water via rainfall percolating down to the aquifer.  As Tucson’s population began to rise, with it the need for water, we started to overpump, or mine, our aquifer.  This lead to lowered water tables, higher costs for water, and a bleak outlook for the future of Tucson and its water needs.

In 2001, Tucson began to mix Colorado River water brought down south via the CAP (Central Arizona Project – which is a canal that brings Colorado River water from northern Arizona to southern Arizona).  Mixing the water with groundwater allowed the water utility to recharge some of the aquifer with CAP water.  Adding CAP water to the mix has allowed the water utility to shut down some pumping wells and as a result the water table has risen in some places.  If you’re interested in learning more about what Tucson’s water plan, please follow this link for more information: http://www.ci.tucson.az.us/water/waterplan.htm.

Central Arizona Project (CAP): Brings billions of gallons of Colorado River water to southern Arizona each year.

However, the population of Tucson has continued to increase and we only have access to a set amount of CAP water, 40 billion gallons of water each year to be exact.  We only use about 22 billion gallons per year currently, but with people moving to Tucson for the sun and the golf, we will exceed our allocation of CAP water in the near future. This means that we’ll have a “water problem” again with no clear solution in sight.

So what can we do?  Well there are a few things we can do to help our water situation.

(1) Water Conservation: The less water we use the less water Tucson needs to use as a city.  We can put in native vegetation in our yards that need minimal watering or no watering  (just imagine never having the mow your lawn again…).  Shut off the tap when we brush our teeth and shave, take showers rather than baths, only wash our cars once in a while rather than every weekend.  Making simple changes will help conserve millions of gallons of water each year, and lower your water bill at the same time.

(2) Reuse Water: Reusing water that we’ve used for clothes washing may seem a little weird, but water your garden with washing machine water (sometimes called “gray water”) can save a lot of water in the long run.  Besides, your plants don’t care what kind of water they get; it’s pretty much all the same to them.  Here’s an example of gray water reuse: http://www.builditsolar.com/Projects/Water/Water.htm.

(3) Rainwater Harvesting: Now this sounds a little hippyish, but rainwater harvesting is big business in Tucson.  Saving rainwater in cisterns to water your yard is easy and cheap (i.e. free, if your subtract the cost of the cistern).  Go to this link for more info: http://www.builditsolar.com/Projects/Water/Water.htm, http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/.

Water is a precious and limited resource, if we all make small changes in our lives, we will have a large impact on conserving this vital resource for the future.

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6 Responses to “Where does Tucson get its water?”

  1. John E. Irby Says:

    Thanks for the info. I don’t know how long ago you posted this, but I’m curious about how the good citizens are responding to the clarion call for water conservation. We recently moved to Marana from Seattle, where water, though cheap and abundant, is still a precious gem in the city’s crown. Though lawns do exist and people do wash their cars and water their gardens, there is a concerted effort by a large percentage of the population to conserve and recycle. The time will come when Seattle rivers and lakes will also be called washes. I appreciate your insights. John

    • desertscientist Says:

      Hi John –
      Thanks for the comment! I’m not sure how people have responded to the Clarion call for water conservation, but I do know that generally, people in the SW are aware that some water conservation is the only way that we’ll continue to live and prosper in the desert. Now, do the act on this awareness? It sounds like people in Marana are making the effort.

      My impression is that voluntary conservation and recycling will only be somewhat effective in the long run. Perhaps the best example of effective water conservation is Santa Fe – The city council mandated water conservation on residents and businesses, now they’re probably the most water conscious city in the US, and proud of it! If Tucson and the surrounding cities followed Santa Fe’s lead, we could be a leader and model city in sensible water use and re-use. We’re on the right track (e.g. legal rainwater harvesting, reclaimed water use on all public fields, and aquifer recharge with CAP surplus), and the efforts of residents to make conservation the norm rather than the oddity will hopefully make law makers take notice.

      I hope this helps.
      -Bryan

  2. Dennis.sumrak@sbcglobal.net Says:

    The CAP water canal seems to be the best immediate supplement to Tucson’s water supply, however, there is some room for improvement.
    Any water exposed to the sun and dry air is going to evaporate. The canal needs to be replaced by a pipeline, or at least covered.
    Also, the concrete lined ditch needs to be maintained to deter the growth of tamarisk (salt cedar). These invasive plants suck huge amounts of water from the ground. The water evaporates through the leaves which excrete a white saline substance.
    Water is our most important resource and action needs to be taken now, before it is too late.

    • desertscientist Says:

      Dennis, you’re absolutely right that CAP is only a temporary solution to a long term problem. Salt Cedar is a huge problem all over southern AZ, and and it seems that only academics are concerned about it…

      The CAP depends highly on snow fall amounts in Colorado, which is expected to vary more in the decades to come. The issue that you bring up with evaporation is one that seems so obvious to you and me, but apparently was not on the minds of the engineers that designed the canal years ago. I was told once by an engineer that was associated with the design that evaporation “doesn’t happen” along the CAP because the water flows at such a slow pace that waves aren’t created to cause excessive evaporation (the laminar flow argument, I guess). If this argument seems totally wrong, it’s because it is. The fact is that any surface that is exposed to the air, especially in AZ, will have a huge amount of evaporation. But there’s no information on how much water is lost due to evaporation along the 300 miles or so of the CAP. This actually brings up the other problem with the CAP – salt importation to southern AZ. Before the CAP was built, Tucson water had a TDS (salt content) of around 250ppm. The quality of the ground water was excellent. With CAP use and reuse of wastewater, Tucson groundwater is now at a TDS of 450ppm. It’s quickly approaching the EPA’s secondary standard for TDS (500ppm) and will soon have to be treated for salt content. In the end, the old saying “there’s no free lunch” rings true.

  3. Fermin Says:

    Fantastic post however I was wanting to know if you could write a litte more on this topic?
    I’d be very grateful if you could elaborate a little bit further. Appreciate it!

    • desertscientist Says:

      Thanks fermin for the comment! What else would you like to know about it? What I find interesting is that the major cities in the sounthwest, for the most part, seem to import their water from other places – makes you think about how sustainable we are (or are not) in light of how we get our water.

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