Recycled Water Controversy: Denver Zoo Backs Off the Purple Pipe

Opened in 2004, Denver Water's treatment plant can produce up to 30 million gallons of recycled water a day.
Opened in 2004, Denver Water's treatment plant can produce up to 30 million gallons of recycled water a day.
Anthony Camera

Denver Water's recycled water program, a supposedly green solution for the increasing demands on one of the metro area's most precious resources, has been coming under some tough scrutiny lately. As detailed in our recent cover story, "What's Killing the Trees in Denver's Parks?", neighborhood groups and park advocates believe that irrigation with reused water is poisoning some venerable park conifers, especially in Washington Park. And in the wake of that controversy, the Denver Zoo has decided to stop feeding recycled water to elephants, rhinos and tapirs in its "crown jewel" exhibit, the Toyota Elephant Passage.

Denver Water's program provides wastewater that’s been sufficiently treated for irrigation purposes at a fraction of the cost of potable water. Since its plant opened in 2004, numerous parks, schools and private entities, including golf courses and the Denver Country Club, have signed up for irrigation with water from the utility's "purple pipe." But while the water is extensively treated to remove solids and then chlorinated, it remains high in sodium — which, over time, can have a devastating effect on some tree species.

Exposing wildlife to recycled water raises other issues. The Rocky Mountain Arsenal National Wildlife Refuge had to jump through extensive hoops with state and federal authorities before it could start using Denver’s recycled water (considered a “degraded” source of supply) to fill its lakes and irrigate bison and bird habitat. After its veterinarians approved the DW product as a safe source of drinking water for animals, the Denver Zoo decided to use recycled water for irrigation, bathing pools and consumption in the Toyota Elephant Passage.  

Bodhi the Elephant in the zoo's $50-million Toyota Elephant Passage exhibit.
Bodhi the Elephant in the zoo's $50-million Toyota Elephant Passage exhibit.
Melanie Asmar

According to zoo spokesperson Tiffany Grunet, there have been no indications of adverse health effects for the animals from recycled water since the exhibit opened four years ago. But recently zoo officials asked the United States Department of Agriculture to review its use of the purple pipe water. "Based on their feedback, the zoo added potable water lines to the exhibit's drinking water," Grunet says.

Federal animal-welfare regulations require that drinking water must meet human consumption standards; the guidelines don't make any effort to distinguish between high-quality recycled water (which Denver Water claims it's providing) versus inferior brands. "Even though we felt strongly that this water was safe and have not seen any issues in its use, it was much easier to add potable water to the area than to try and change a federal agency's definition," Grunert says.

Recycled water is still used at the exhibit for the bathing pools, irrigation and cleaning purposes. But an elephant who gets a snootful of the salty stuff while showering can get a fresh-water chaser from the potable supply. At present, the evergreens in Washington Park have no such option. 


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