Recent news about water use has highlighted a possible oversight in the general knowledge about data centers.
Why do data centers use water for cooling?
Simply put, heat absorption and rejection. Most server equipment produce a lot of heat when in operation, and the heat needs to be rejected. From the rack, the hot air is channeled to a hot aisle, and the hot aisle is usually a chimney to a plenum to move air to a cooling unit or also exhausted from the building. The cooling unit could be a CRAH/CRAC/Fan wall with coils/Kyoto wheel/etc, and this is where water is first used if there is a CRAH using evaporative/adiabatic cooling. Other cooling units do have water to absorb the heat, but they are in a closed loop and require very infrequent water addition. Once the hot air rejects this heat to water inside the cooling unit closed loop, this water is moved to a chiller or heat exchanger to be transferred to a condensate loop, then getting rejected outside of the building. It can be rejected to dry coolers, which are closed loop, but can possibly use water for adiabatic supplement spray on the coils to lower temperature, or it can go to cooling towers, which are recirculating water over a media (to increase surface area) to cool water via evaporation.
There can easily be data centers that use no additional water for cooling aside from what is in closed loops. There are even data centers that cool via geothermal wells, rejecting the heat underground or into a local body of water.
For data centers that DO use water for cooling, the water is used in systems and equipment that reuses the water until it is evaporated or dumped to the waste drains due to high water salinity. Water is added to the sumps/basins of the cooling units while the unit is in operation.
Of the data centers that do use water, depending on geography of course, it might only use the water cooling mode during the warmest months of the year, otherwise using outside air for cooling.
Water is a great tool for heat absorption and rejection, and help reduce the use of chiller or air conditioning refrigeration based systems.
Data centers source the water from either wells on site, the local water provider, or even reclaimed water sources. Reclaim water (polished and treated grey or black water) is popular since it does not impact the potable water supply and is generally less expensive than industrial or potable water per liter/gallon.
Obviously data center that do not use water for cooling still use water for typical facility uses like drinking water, bathroom water, cleaning, water based fire systems. But these water numbers are usually very low compared to what is needed for cooling.
Even with AI data centers and liquid cooling, water will still be used if the design uses open loop cooling towers or evaporative cooling elements.
Bottom line, some data centers may use water while others don’t use water for cooling at all. It is heavily influenced by design and geography choices, and not all data centers are the same water guzzling big baddy they make out in the news.
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