Staff at The Conservation Foundation attended the UIC conference on data centers and water reuse on Friday, May 8th in Chicago. The main takeaway from the conference was that data centers have a tremendous need for cooling water — currently to be met using potable water. Approximately 80% of this cooling water is turned into steam (as one supportive speaker put it, they’re “expediting the water cycle”). This approach to cooling is problematic for two main reasons. First, the water used is far higher quality than necessary, refined to drinking standards. Second, withdrawals from Lake Michigan are capped by the Great Lakes–St. Lawrence River Basin Water Resources Compact, which allocates a fixed quota to Illinois.
The conferences proposed solution to both issues is to use treated wastewater effluent instead of potable water. The region already produces substantial volumes of effluent that, with additional treatment, could be repurposed for cooling. This strategy would reduce wastewater discharges, reduce draw on the quota, reuse a “wasted material,” conserve high-quality drinking water, provide a new revenue stream for wastewater treatment plants (WWTPs), and position the area as a leader in water reuse.
While the logic is sound and the concept commendable, several important considerations were not addressed:
1. Flow: Waste water effluent is already reused, as rivers! Indeed, a significant portion of local river flow comes from WWTP effluent, which can make up the majority of flow during summer months. Reducing this discharge will negatively impact aquatic ecosystems. Moreover, WWTP permits are often tied to maintaining aquatic life standards, meaning reduced flow could make long-term compliance more difficult. For example, during dry summers, 70–90% of Salt Creek’s flow is treated wastewater.
2. Pollution: Ironically, reducing wastewater discharges will increase concentrations of river pollutants from stormwater runoff, including bacteria and chlorides (salts). These are typically diluted by wastewater effluent.
3. Residual Brine: The cooling process (steaming) will generate concentrated residues of pollutants — essentially everything dissolved or suspended in the effluent water. How this brine will be managed and disposed of remains unclear, though this concern may be secondary to the two above it may compound them.
This doesn’t mean that reusing treated wastewater for data centers is a bad idea — far from it. However, it isn’t quite the environmental “slam dunk” it’s sometimes made out to be. We need to consider the secondary and tertiary impacts carefully, and on a case-by-case basis.
Stephen McCracken
DuPage River Salt Creek Workgroup Director
The Conservation Foundation