- Consumptive Water Use
- The portion of withdrawn water that does not return to its source, chiefly the water evaporated in cooling. It is the figure a stressed basin cares about most, as distinct from withdrawal, which counts all water taken in including what is later returned.
- Cooling Optionality
- The ability to change which resource a facility spends, water or watts, as conditions change, built through reclaimed water, hybrid and liquid cooling, seasonal switching, and diversified siting. It is what lets an operator absorb a drought year and a carbon rule at the same time.
- Evaporative Cooling
- A cooling approach that rejects heat by evaporating water in a cooling tower, exploiting the large heat absorbed during the liquid-to-vapor phase change. It is energy-efficient but consumptive, spending water that leaves the local watershed as vapor.
- License to Operate
- The combination of formal permits and informal community consent a project needs to be built and run. For water, it depends on the specific basin, regulators, and neighbors, and it is earned before it is needed and cannot be bought back once lost.
- Power Use Effectiveness
- The ratio of a facility's total energy use to the energy that reaches its computing equipment; a perfect score is 1.0. Because the cheapest way to lower it is often heavy evaporative cooling, a strong figure can quietly reward a heavy water draw.
- Reclaimed Water
- Treated municipal wastewater redirected to cool a data center instead of being discharged. It keeps the energy benefits of evaporative cooling while removing the facility from competition with drinking-water supply, often defusing community opposition.
- Source vs. Site Water
- Site water is what a facility consumes in its own cooling plant; source water also counts the water consumed upstream at the power stations generating its electricity. Going dry can shrink the site figure while growing the source figure, relocating water rather than saving it.
- Water Use Effectiveness
- A metric for the volume of water a data center consumes per unit of computing energy delivered, usually stated in liters per kilowatt-hour. It is the water counterpart to power use effectiveness, and reading the two together is the only honest way to judge a cooling strategy.