Sunday, November 19, 2023

Water and Data Centers

We all know that data centers use huge amounts of electricity to power their millions upon millions of chips. However, data centers also use large amounts of water for cooling systems, which ensure that the heat produced by these massive facilities is controlled.

Data center cooling systems use large amounts of water to operate. These systems includes cooling towers, chillers, pumps, piping, heat exchangers / condensers, and air conditioner units in the computer rooms. Additionally, data centers need water for their humidification systems (to avoid static discharges) and facility maintenance. Data centers are either water-cooled or air-cooled, with water-based cooling using evaporative cooling systems more common, particularly for large data centers simply because it is more efficient and effective. Direct contact cooling systems using evaporation can remove and release all of the heat produced inside a data center from the servers and other IT equipment.

In a water-cooled system, water-cooled chillers and cooling towers located on top of the data center roofs produce chilled water, which is delivered to computer room air conditioners for cooling the entire building. In 2021, when Prince William County looked at water consumption for its 25 operational data centers at the time it found that water use varied by season and ranged from about 0.2 to 0.5 gallons per square foot per day. The data centers that Prince William looked at were all relatively small 100,00-250,000 square feet- nothing like the hyper centers being built now. Today, data centers seem to start at a million square feet and move up from there with multiple building campuses.  How water use scales up in multi-story data centers is unknown.

For cooling purposes, data centers typically use potable water, on-site groundwater, or surface water, and rainwater capture systems. Prince William county believes that most data center water comes from potable water supplies. In Loudoun, to some extent, they source non-potable / recycled water, which is treated sewage. In Prince William the treated sewage from UOSA is already used by Fairfax Water to supplement water supply to the Occoquan Reservoir for our drinking water supply.

Water used to cool data centers is either consumed, meaning it evaporates into the atmosphere via the data center’s cooling towers or is discharged, as industrial wastewater, usually to a local wastewater treatment plant. Effective water treatment, either on-site or off-site through a wastewater treatment plant, means that the water can be reused in the cooling system several times, if the water quality (e.g., hardness) is acceptable. Of course, softening the water could help, however, it brings ,pre salt into the waste water.

Data centers reuse water by recirculating the same water through their cooling systems multiple times while replenishing what evaporates. According to Google, this practice saves up to 50% of water when compared with “once-through” cooling systems. However, eventually this reused water needs to be replaced with new water, due to mineral scale formation which will damage the cooling equipment or once the conductivity of the water is too high which could damage the IT equipment. The need for new water results from the build-up of calcium, magnesium, iron and silica, which become concentrated over multiple evaporative cooling cycles.

Amazon Web Services (AWS), Google and others have committed to  being “water positive by 2030,” returning more water to communities and the environment than it uses in its direct operations. This is a very interesting concept. You see, there is no mechanism on Earth for creating or destroying large quantities of water. All the water we have is what's been here, literally, forever- since the planet was formed 4.5 billion years ago. Of all the water on earth only about  3% is fresh: however, only ½% of the water on earth is available for mankind to use. The rest of the fresh water is locked away in ice, super deep groundwater or polluted beyond redemption.

Where exactly are Amazon and Google going to get this excess water they plan to return more of than they use to communities. Obviously, they would have to take it from another watershed or somewhere else. Water is a zero sum game here. No one is making water. The available supply of fresh water is continually renewed by the hydrologic cycle or artificially. Rain drops falls fall to earth and will evaporate, infiltrate into the soil, recharge groundwater or flow along the ground to a stream and ultimately flow into rivers and to the ocean-moving always moving. That is the most basic description.

Building data centers can interfere with the hydrologic cycle.  Covering once open wooded areas with impervious surfaces reduces the recharge of groundwater which impacts stream flow. Changing the use of the land, covering it with buildings, driveways, roads, walkway and other impervious surfaces will change the hydrology of the site reducing groundwater recharge in the surrounding area increasing stormwater runoff velocity and quantity. Once the hydrology is destroyed by development, it cannot be easily restored, if at all.

The Occoquan Reservoir is fed by the Occoquan River which receives up to 40 million gallons a day of the treated discharge of the Upper Occoquan Sewage Authority treatment plant, UOSA.  which  discharges to the river upstream of the Occoquan Reservoir.  A significant portion of the flow (especially during dry periods) into the reservoir is recycled sewage. This treated wastewater is from areas supplied by the Potomac River or lake Manassas so you do not end up with constantly recycling and concentrating the same impurities into the drinking water supply.

In addition, the Occoquan Reservoir receives stormwater runoff, precipitation from the Occoquan Watershed which covers portions of Loudoun, Fairfax, Fauquier, and Prince William counties and feeds the streams and creeks that feed Bull Run and the Occoquan River. Obviously, the Amazon Web Services (AWS) commitment “to be water positive by 2030, returning more water to communities and the environment than it uses in its direct operations” means that either they are incredibly naive about water or plan to take water from another place or disrupt the hydraulic balance to fulfill this pledge.


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