Resource // Definitions
Data Center Water Glossary
Plain-language definitions for the cooling, water-quality, treatment, utility, and project terms used throughout data center water reuse.
- Adsorption
- The accumulation of dissolved substances on the surface of a solid media. It differs from absorption, in which a substance enters the volume of another material.
- Blowdown
- Cooling water intentionally removed from a recirculating system to control the concentration of dissolved minerals and other constituents.
- Concentrate
- A treatment residual stream containing constituents rejected or separated from the recovered-water stream, such as reverse-osmosis reject.
- Conductivity
- A measure of water's ability to conduct electrical current, commonly used as an operating indicator of dissolved ionic concentration.
- Consumption
- Water withdrawn but not returned to the immediate water system, commonly because it evaporates or becomes incorporated into another stream.
- Cooling-Tower Makeup
- Water added to replace evaporation, blowdown, drift, leaks, and other losses from a cooling tower system.
- Cycles of Concentration
- The ratio of a representative dissolved constituent or conductivity in circulating or blowdown water to the makeup water.
- Drift
- Small water droplets carried out of a cooling tower with the exhaust air. Drift eliminators are used to reduce this loss.
- Electrostatic Capture
- Attraction between charged or polar species and a treatment media surface. Performance depends on water chemistry and media properties.
- Evaporation
- The conversion of liquid water to vapor. In evaporative cooling, this phase change rejects heat and is a consumptive water use.
- Fit-for-Purpose Water
- Water treated to quality requirements appropriate for a defined use rather than automatically treated to drinking-water standards.
- Hardness
- Primarily dissolved calcium and magnesium, which can contribute to mineral scale under concentrating cooling-water conditions.
- Ion Exchange
- A treatment process in which selected dissolved ions in water are exchanged with ions held on a resin or other exchange media.
- Makeup Water
- Replacement water added to a system to offset water lost through evaporation, blowdown, drift, discharge, or leakage.
- Parallel Treatment Trains
- Multiple treatment trains arranged so capacity can be divided, expanded, maintained, or regenerated without relying on one process line.
- POTW
- Publicly owned treatment works: a municipal wastewater treatment system that may include its connected sewer collection network.
- Pretreatment
- Treatment or control applied before discharge to a municipal wastewater system or before a downstream water-treatment process.
- Reclaimed Water
- Wastewater treated for beneficial reuse in an appropriate application rather than discharged after a single use.
- Recovery Rate
- The percentage of feed water converted into the desired recovered-water stream. The remainder leaves as residuals, concentrate, or other losses.
- Regeneration
- Restoration of treatment-media capacity through a defined physical or chemical process so the media can return to service.
- Residuals
- Concentrated liquids, sludges, spent media, filter cake, solids, or other materials separated during water treatment.
- Reverse Osmosis
- A pressure-driven membrane process that rejects many dissolved constituents and produces a lower-salinity permeate plus a concentrate stream.
- Silica
- A naturally occurring constituent that can become a difficult scale-forming material as water concentrates under certain chemistry and temperature conditions.
- Total Dissolved Solids
- The combined dissolved inorganic and organic substances in water, commonly abbreviated TDS and reported as a concentration.
- Water Balance
- An accounting of water entering, leaving, accumulating within, and moving between processes across a defined system boundary.
- Water Usage Effectiveness
- A data center metric, commonly abbreviated WUE, calculated as annual site water usage in liters divided by annual IT equipment energy in kilowatt-hours.
- Withdrawal
- Water removed from a surface-water, groundwater, municipal, reclaimed, or other supply source for use by a facility.
- Zero Liquid Discharge
- A system boundary in which routine process wastewater does not leave as a liquid discharge; concentrated residuals or solids still require management.