Every day, 5 million gallons of water from Santa Fe's toilets, sinks and gutters flow into the Paseo Real Wastewater Treatment Facility. There the water gets churned and filtered, settled, sifted, aerated and zapped by ultraviolet lights until it finally leaves the plant again through a pipe on the southwest side, clean enough to pipe back up to the city's golf courses and green spaces and to flow down the Santa Fe River.

Some of that water seeps through the riverbed into the underlying aquifer and some of it is used to irrigate farms and ranches in the downstream communities of La Cienega, La Bajada and Cochiti Pueblo. But the city has other, grander plans for wastewater that are raising concerns among some downstream users and environmental advocates.

Last week in La Cienega, city and county employees, members of local environmental groups, and downstream ranchers and farmers who make up the Santa Fe River Community Collaborative met in the La Cienega Community Building to discuss a range of issues that impact the river downstream from the treatment plant, including a proposed return flow credit pipeline that is part of the city's strategy to address future water shortages.

It's a proposal that has quietly been in the works for years, but has recently started to generate both more scrutiny and support.

In response to a 2015 study indicating the likelihood that Santa Fe could face indefinitely prolonged drought conditions and water scarcity issues as early as 2050, the city got to work figuring out how to get even more bang for its water buck by more efficiently putting effluent water to use.

An environmental engineering firm hired by the city to analyze alternative strategies for reusing wastewater identified using the effluent for return flow credits as the most efficient and cost-effective option among several possible alternatives that include purifying effluent back to potable standards for municipal use.

Under the return flow credit proposal, effluent would be diverted into a pipeline and discharged back into the Rio Grande just downstream from the Buckman Direct Diversion Water Treatment Plant that takes water from the Rio Grande and pipes it up toward city and county taps.

So far, the city estimates that building the pipeline would cost about $20 million. It has set aside $1.2 million in the capital improvement budget for preliminary engineering design and permitting, and is seeking grants to cover further costs of construction.

If the project meets muster from state and federal officials, the city proposes to divert an extra acre-foot of fresh water from the Rio Grande for municipal use in exchange for every acre-foot of effluent that it released back into the river through the pipeline. This is what makes it an attractive option for the city, especially during the winter months, explains Water Diversion Director Jesse Roach.

"The return flow pipeline is intended only for returning water that was imported from outside of the Santa Fe Watershed to the Rio Grande," he tells SFR in an email, adding, by phone, "It's really the best option for getting the most out of our water and would make it easier to develop other reuse strategies down the road. All those other alternatives are still on the table, but at the moment the pipeline is the lowest hanging fruit and the most effective economic, environmental, and social option we have."

Not everyone agrees that this is the best way for the city to reuse its water.

At the community meeting last week, Neil Williams, who identified himself as an engineer and member of the local Sierra Club, opened the meeting by highlighting what he sees as red flags in the city's return flow credit pipeline proposal.

"I don't think that a lot of the flaws of this project have been actively discussed," said Williams, listing water treatment standards—which are lower for the Rio Grande than they are for the Santa Fe River—costs of the project, and lack of outreach to downstream users as reasons for concern.

But mostly, Williams was concerned that the city's report did not adequately address dependence on groundwater and the depletion of the local aquifer, or the possibility of using the city's effluent water to develop aquifer storage and recharge strategies.

Bill Schneider, the water resources coordinator for the city, countered that the city needs to consider how it will provide residents with water in the unlikely case that the water supply in the reservoir becomes unusable, such as if a fire were to occur in the Santa Fe watershed, contaminating one of the city's primary source of fresh water.

In the case of short-term water emergencies and long-term shortages, the city might have no other options than to take more water from the Rio Grande, Schneider said at the meeting, adding that purchasing more Rio Grande water rights would be a much more costly and unreliable option than putting the return flow pipeline into action ahead of the game.

The proposed pipeline is not yet under construction and is still in the proposal stage, and the city promises more public input sessions are to come this fall.