The short answer
Data center cooling water does not all go to one place. In a cooling tower system, part of the water evaporates to reject heat. A separate liquid stream leaves as blowdown to control mineral concentration. Other water may be used in treatment, humidification, or facility operations; whether it becomes discharge depends on the system.
That distinction matters because evaporation and blowdown are not interchangeable. Evaporation leaves as vapor. Blowdown remains liquid and can be treated for reuse.
How heat reaches the cooling tower
The U.S. Department of Energy describes a common water-cooled path:
- IT equipment generates heat.
- Air handling or liquid loops move heat away from the servers.
- A chilled-water system carries the heat to the chiller.
- The chiller transfers heat to a condenser-water loop.
- The cooling tower rejects that heat to the atmosphere through evaporation.
Not every data center uses this architecture. Some rely more heavily on outside air, dry coolers, direct liquid cooling, or hybrid systems. The water pathway depends on the design.
Evaporation versus blowdown
| Water stream | What happens | Can it be recovered as liquid? |
|---|---|---|
| Evaporation | Water changes to vapor as the cooling tower rejects heat | Not by a blowdown treatment system |
| Blowdown | Mineral-concentrated liquid water is discharged to protect cooling-system chemistry | Yes, if treatment can remove the accumulated minerals |
| Drift | Small droplets can leave with tower exhaust; controls are used to limit it | Not normally treated as a recoverable process stream |
| Discharge | Liquid water leaves the site or enters wastewater treatment | Depends on chemistry, infrastructure, and treatment requirements |
Cooling towers continuously recirculate water. As pure water evaporates, dissolved minerals remain and become more concentrated. Operators remove a portion of the circulating water as blowdown so scale, corrosion, and biological risks remain manageable.
Withdrawal, consumption, and discharge are different
EPRI distinguishes three related quantities:
- Withdrawal: water brought into the site.
- Consumption: water not returned to the immediate water system, primarily because it evaporates.
- Discharge: water returned to a utility or the environment after use.
A site can withdraw a large volume while consuming only part of it. It can also consume water indirectly through electricity generation. These quantities should be reported separately.
Why cooling design changes the answer
Cooling architecture, climate, IT load, utilization, and operating strategy change both water and energy use. Evaporative cooling can reject heat efficiently with less fan energy and footprint, but it consumes water through evaporation. Dry cooling can reduce direct site water use but may require more energy or equipment under some conditions.
LBNL’s review identifies cooling type, climate, utilization, server efficiency, infrastructure efficiency, and grid water intensity as major determinants. There is no single water-use number that applies to every data center.
Which water can RECOVER address?
NONA RECOVER targets liquid cooling tower blowdown, not evaporation. It continuously demineralizes cooling water so the treated stream can return to the loop rather than being dumped.
RECOVER uses Ion Concentration Polarization, an MIT-patented alternative to reverse osmosis, and recovers 90% of cooling tower blowdown on site. It works alongside the cooling towers already at the facility.
For a site assessment, measure makeup water, blowdown flow, cycles of concentration, cooling load, operating schedule, and local water and sewer rates. Those inputs determine the practical water and cost opportunity.