Rethinking Water Quality in a Drying World

By Nicholas Hodder.

The San Pedro River flows northward from the mountains in Sonora, Mexico, crosses the border into Arizona, and continues 140 miles to its confluence with the Gila River in Winkelman, Arizona. It is the last major, undammed desert river in the American Southwest. It hosts over 300 species of migratory birds, including over 100 species that breed along the river. That accounts for two-thirds of the avian diversity in the entire United States. Tragically, this ecologically significant river is in danger of drying up.

The Drying River and the Depleted Aquifer

The San Pedro River, in a sense, is already dry. For many stretches of the river, no water flows on the surface except in direct response to rain, often during the monsoon season. But this does not mean the river is dead. The majority of rivers in the southwest are dry for part of the year, and even when appearing dry, water flows beneath the surface in the porous ground around the riverbank. Vegetation lines the banks of these rivers, surviving off the water. These lush riparian zones (zones adjacent to a river) are very significant to the region’s ecology. Although riparian habitat covers only 1% of the Southwest, it supports 50% of breeding bird species and is often where migrating birds stop to feed. Cottonwood trees—the largest tree in Arizona—also line the banks of the San Pedro, and they only survive because of the water flowing beneath the surface. 

Decades of agricultural pumping in the San Pedro Valley is depleting the aquifer. The aquifer is far deeper than the water under the San Pedro, but the two systems are connected. As the groundwater levels sink lower and lower, the water under the San Pedro’s bed is depleting as well. If nothing is done, the lush zone of vegetation around the river will dry up, the cottonwoods will die, and the southwest will lose one of its treasures.

Recharging the Aquifer

The easiest solution to save this river, and its ecologically significant riparian zone, is to recharge the local aquifer with effluent from the local town—Bisbee, Arizona. Effluent is wastewater; it is a byproduct that every city creates. However, under Clean Water Act (“CWA”) precedent, if Bisbee injects that wastewater into the aquifer, and it travels into the San Pedro, the CWA treats it as if the city dumped the wastewater directly into the river itself.

The city must comply with a complicated and expensive permitting regime if it wants to discharge effluent into a river under the CWA. The CWA is focused exclusively on water quality, and the permitting regime reflects this. Therefore it will be difficult to receive a permit unless the effluent is treated to comply with CWA standards. Although this is theoretically possible, the process of treating effluent can be prohibitively expensive for small towns like Bisbee. Admittedly, the CWA is rightly concerned with pollutants traveling into existing rivers and harming the ecosystem. But in this situation, the choice is between accepting some pollution or allowing a river to die. And the CWA does not contemplate discharging dirty water to save a river.

Additionally, violating the CWA by not getting the proper permits can result in fines of $25,000 per violation per day. An obvious solution would be for Bisbee to inject clean water into the aquifer. However, water in the southwest is hard to come by, and effluent is a consistent, available source. In this situation, the CWA—a law designed to protect this nation’s waters—is paradoxically getting in the way of saving a river.

The Clean Water Act

We have a regulatory regime that addresses only one aspect of the problem—water quality—while ignoring an equally important facet—water quantity.  How did we get here? The CWA was created in the 1970s as a response to rampant pollution in mostly east coast rivers. A river in Ohio was so polluted it famously kept catching on fire. This was before major populations out west began depleting their aquifer resources, and before the mega-drought began that is currently gripping the southwest.

At the time Congress passed the CWA, water quantity just did not seem like that big of an issue. However, we now need to reframe how we protect rivers to address this growing concern. The Southwest is in the middle of the worst drought it has seen in the last 1,200 years. The water levels in Lake Mead, outside of Las Vegas, have declined to 35% of the reservoir’s total volume. The lower states in the Colorado River basin suffered cuts in their water supply stemming from shortages on the river. Water quantity may not have been an issue when the CWA was passed, but it is now.


The San Pedro might be the first casualty of bifurcating these concepts, but it does not have to be. The permitting system needs to be amended to confront this issue. What that looks like in practice is beyond the scope of this blog post; but some flexibility needs to be built into the regime to address rivers that are in danger of drying up. After all, what is the point of keeping a river clean when the river itself ceases to exist?    

"Dry River Bed" by Eric Vondy is marked with CC BY-NC-ND 2.0.