Rainwater Harvesting, Arizona Style

Chris Brooks has a post on proposed legislation in Arizona that would have created incentives for large-scale rainwater harvesting and groundwater recharge. The idea was to give people water rights to the resulting water stored in the aquifer.

As Chris notes, there are a couple of problems. First, some of the rainwater you harvest and store underground would have otherwise drained to a river. Where downstream users have water rights. This the classic conundrum that dogs our discussions of the issue here in New Mexico. It’s not free water, and just because it runs off of your city doesn’t mean it’s being “wasted”.

Chris raises a second, much more nuanced and interesting issue:

Looking at the original legislation, it seemed pretty silly to me that you would go to the expense of harvesting rainwater just to put it in the ground, then pump water back out of the ground to provide to customers. Seems a lot simpler to just spend that money buying rain barrels for people they could use to harvest their own water to then use in place of potable water. In theory, that would permit water providers in the area to reduce their pumpage, thereby cutting into the amount of the overdraft. But it doesn’t really work out that way. Having decisions made by thousands of individual homeowners is not how water providers like to manage their water supplies (although to some extent it is kind of like that now). And having current customers reduce usage doesn’t mean that water will stay in the ground, it will just be used somewhere else or at some other time. This also doesn’t create more renewable water that satisfies the requirements of state law, so it can’t help areas that need renewable water to keep growing.

In the end, the legislation went nowhere. Instead, they formed a commission to study the issue!


  1. Seems to me the gridlock is on the ownership of rainwater not so much the sensible use of water.
    If by using rainwater I replace water being pumped from a distance I save on energy as well as water itself is used more efficiently without ‘losses’ due to evaporation et al.
    We have a rainwater harvesting law in place here in Bangalore,India and all is well for us.

  2. With respect to barrels for homeowners to store rain: how many would be required to make a difference? Where would these be stored? Would each home need pumps to effectively use the water? In contrast, to harvesting on such a small-scale, the Arizona State Land Department (or various Indian tribes) could dedicate millions of acres to capturing rain water to be used on the land it controls or to be sold to others.

    The Prescott Daily Courier had several articles in which a consultant was quoted as saying (if memory serves me) that 98% of the rain in the Prescott Active Management Area ends up as evapo-transpiration. If correct, the issue of water draining to streams may not be a big deal.

    What I did not see however is any information on how much is evaporation and how much is (plant) transpiration. I wonder how plant life would be affected by rainwater harvesting.

  3. @mahtso – The rain barrel example was basically shorthand for the kind of low-impact, distributed rainwater harvesting that is slowly becoming more typical. It could involve barrels or cisterns or just landscape modifications. Just depends on what you want to do with the water. The problem with the legislation as originally written was that it would necessitate larger-scale harvesting to be worthwhile and that is the sort of thing that scares downstream water rights holders – regardless of how real the threat is. As you indicate, most precipitation in our climate doesn’t make it to a river or an aquifer under normal conditions – it evaporates or is used by vegetation. I don’t know if anyone has ever tried to quantify the split between those destinations.
    Also, I should note that the commission has not been authorized yet. The legislature is still in session and, to my knowledge, this bill still needs to be passed and sent to the governor.

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