A Pretty Impressive Graph showing what Tucson Water has been doing with Renewable Water

At a recent meeting I attended at Tucson Water, their hydrology staff gave a presentation on where our water is coming from these days.  One graph in particular really drew a reaction from those in attendance:

This does require a bit of context though.  What is being shown is the total amount of water produced by the utility and provided to its customers.  This is then broken down into the different types of water that are produced: groundwater, CAP water, and reclaimed water.  The main purpose of the chart is to show that the proportion of our water that is coming from groundwater is way down since the beginning of the 21st century.  In the late 1990s Tucson Water was pumping over 100,000 acre feet of groundwater to provide potable water to its customers.  Today they are pumping just over 10,000 acre-feet.  The other key takeaway is that the water demand of their customer base has fallen way off since the middle of the last decade - to the point where potable water demand is at roughly 1994 levels.  This has caused some financial challenges for the utility, as I have discussed here and here.

Drilling down a bit further into those number it should be noted that the amount of pumping from wells by Tucson Water is basically equal to that total demand number.  The reason for this is that both the CAP water and a large portion of the reclaimed water is recharged into the aquifer in basins, then recovered via wells to be put into the delivery system.  This is an aspect of Arizona groundwater law that not everyone knows about - when renewable water is put into the ground by recharging it can be pumped back out and is still considered renewable water, even if the location where it is pumped out is not hydrologically connected to the location where it was put into the aquifer.

Fortunately, that is not what Tucson Water does.  Their facilities are constructed so that their recovery wells are largely pumping back out the water that they put into the ground.  When you are producing as much water as they do, it would be exceedingly unsustainable to do it any other way.

The process of getting our CAP water into the pipes that serve customers has been a long, slow one.  That blip of CAP use in the 90s was the city's first attempt at serving CAP water to customers: by treating it and putting it directly into the pipes.  That didn't go so well.  The different chemistry of CAP water caused home piping to corrode and brown water came out of people's taps.  The city ended up shutting down the CAP treatment plant and returning to groundwater for several years.  Construction of the recharge infrastructure was what allowed the city to begin using its CAP water again, which gradually ramped up over the past 13 years.

It's a real success story, that I only scratched the surface of in this post.  If you want to see the whole power point presentation from the meeting it can be downloaded here.  Lots of info about Tucson's management of our water supplies can be found here.