PW Water Comments Incomplete and Misleading

On the Prince William Water website, you can find an information page on data centers. The information while true is incomplete and somewhat misleading. Whether this is intentional, I do not know. I think it was intended to be comforting. Over the next couple blog posts I will more fully discuss the issues. In the blog post below the bold face print is what Prince William Water posted the rest is my discussion.

Do data centers use water for cooling?

Data center developers and operators use different cooling technology – water cooled or air cooled – based on several proprietary factors. The decision about which cooling technology is used is owner-determined and project-specific. 

Data centers generate heat. Servers and their related equipment generate a considerable amount of because every watt of power used by a server is dissipated into the air as heat. Feel the bottom of your own computer (this is why it is hard to keep the cat off the computer). The amount of heat output per server varies, depending on the type of chip and configuration. If the equipment gets too hot it will be destroyed. Data Centers are cooled using either air conditioning (electricity) or evaporative cooling (water). Evaporative cooling is more efficient and effective. In hot regions and with AI chips water cooling is preferred both for cost and heat removal ability.

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. Some of this water can be recycled through the system more than once, 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 could damage the cooling equipment or increase the conductivity of the water which could create static and damage the IT equipment.

The need for new water results from the build-up of calcium, magnesium, iron, silica, and salt which become concentrated by evaporative cooling cycles. The amount of water data centers consume also fluctuates based on seasonal weather conditions. Facilities typically use less water during the winter months and more during the summer months. We’ve seen this effect in water use data from Loudoun County.

Loudoun Water presentation to ICPRB showing seasonality of water use

Data centers are primarily located in the western areas of Prince William County. Western Prince William County drinking water is supplied by Fairfax Water’s Corbalis Water Treatment Plant, which draws from the Potomac River. Once used by data centers in western Prince William County, the wastewater is treated at the Upper Occoquan Service Authority Water Reclamation Plant and released as reclaimed water to the Occoquan Reservoir. In this water cycle, water used from the Potomac is reclaimed and released into the Occoquan Reservoir, adding volume.

The discharged cooling water that is too salty to continue reusing in the data centers is sent to UOSA wastewater treatment plant. This plant is not equipped to remove salt and minerals and so ultimately those excess minerals are mixed with all the other treated wastewater and released into the Occoquan River and flows right to the Occoquan Reservoir. During summer months and periods when there is no rain the treated wastewater is a significant and growing proportion of the water in the Occoquan Reservoir. For two generations UOSA has been a significant portion of the drinking water supply from the Griffith Plant which supplies eastern Prince William County through both American Water and Prince William Water.

The other sources of water to the Occoquan Reservoir are the streams (and groundwater-more on that Thursday) of the Bull Run water shed that flows into Bull Run and the streams (and groundwater) in the Occoquan Watershed that ultimately flow into the Occoquan River.

How much water do data centers use?

Data center water consumption depends on factors such as facility size, cooling type (water intensive or air cooled) and outdoor temperature. Prince William County had 34 data centers in 2023. Seasonal weather affects data center water use; facility water use is lower in winter and higher in summer. In 2023, data centers in Prince William County consumed approximately 1.4% of Prince William Water's average daily water demands and 6% of its maximum daily water demands.  

The industry treats water use (and everything else) it as a trade secret. However, Prince William Water 2023 financial report gives the water use for Prince William Water, 11,387,000,000 gallons for that year. The 34 data centers that existed in 2023 used in the neighborhood of 159,400,000 gallons of water (from Prince William Water- in addition a single data center user reported 35,000,000 gallons to DEQ from a well in Manassas).  Prince William Water also reports that 6% or 2,700,000 of the 44,400,000 peak use summer day was to data centers. It has been estimated that data center square footage will more than triple off of the 2023 number in the next 15 years.  

from PW Water 2023 Financial report

It should also be noted that the peak use day probably happened during the summer drought of 2023. The rainfall totals for May, June, July and August of 2023 were all below average in our area.  The reference year I used was from the  fiscal year 2023 which ended on June 30, 2023. The existing data centers in Prince William County and those coming on line in the next decade will continue to be supplied by the Corbalis Plant drawing its water from the Potomac River.  The Washington, DC, metropolitan area (WMA) is home to almost five million people, the federal government and commercial operations that support all of the people and government.

The regional water suppliers share the Potomac River as the sole major regional water resource. The waters of the Potomac are not infinite. Thirty-five years ago the regional water companies and came together to form the Interstate Commission on the Potomac River Basin (ICPRB) and a cooperative agreement (Co-Op) for planning and sharing the water resources available regionally.

 One of the most important functions of the ICPRB is that every five years they conduct a study to evaluate whether available water resources will meet forecasted water demands. The water resources of the Potomac River are limited. The most recent study accounted for both climate change and growth and  found that if droughts become much more severe as predicted in the climate forecast, even with the addition of the reservoirs in various stages of planning and construction: Vulcan Quarry, Milston Quarry, Travilah Quarry and Luck Stone Quarry B (adding over 13 billion gallons of water storage) and using water restrictions and demand management the Potomac River may be unable to meet combined water supply needs and the environmental flow-by at Little Falls during periods of drought. Even more water storage would be needed to ensure that during dry periods there is water for everyone.

Water demand from the Potomac River averaged 453 million gallons per day (MGD) for the for the last period reported in the study (2014-2018). The ICPRB projects that average annual water demand will increase to 501 MGD (10%) by 2040 and to 528 MGD (16%) by 2050. It is not clear how many data centers were included in the projections (if any), but the good news is that the ICPRB has a history of not adequately accounting for the adoption of low flow toilets and water efficient appliances so there may be some wiggle room in the forecast.

Nonetheless, the demand for water will increase. A wide range of evidence indicates that the earth has been warming over the past century and patterns of precipitation are changing.  These trends are likely to continue.  Likely changes in temperatures and precipitation will affect the availability, use, and management of water resources. The climate projections indicate that the mid-Atlantic states, on average, are becoming and will continue to get “wetter.” Climate scientists also warn, however, that floods and droughts will become more severe.  Our water infrastructure will have to include more water storage to meet a larger demand during longer droughts.

The summer of 2024 was a warm and dry. Though Hurricane Helene brought rain to us at the end of September, it was followed by the longest dry period on record -nearly 40 days. We are experiencing drought. Prince William Water and all regional water companies are attempting demand management because the flow of the Potomac River Water’s social media post featured November 7^th  read in part:

“Metropolitan Washington remains under a Drought Watch, following several months of low rainfall with dry conditions expected to continue throughout the fall and winter months. The Drought Watch was enacted in July by the Metropolitan Washington Council of Governments (COG). 

A "watch" is the second level of COG’s four-stage regional drought response plan, designed to monitor water levels and address drought conditions throughout the year. Despite the current conditions, regional officials emphasize that there is an adequate supply of water in the Potomac River and back-up reservoirs.

We encourage customers to practice wise water use for indoor activities—like washing clothes and dishes, showering, and brushing your teeth--and for outside uses like watering their lawns or washing their cars. Prince William Water has wise water use tips available below. If you are continuing to water your lawn, we recommend following the outdoor watering schedule below…” Prince William Water goes on to give an alternate day watering schedule and recommendations on how homeowners can reduce water usage.

Everything is fine, but please conserve water. Meanwhile, Prince William Water states that they can purchase additional water supply capacity from Fairfax Water.

from Prince William Water

Can Prince William Water support the water demands of proposed data centers and residential/commercial development included in the Prince William County Comprehensive Plan and recent land use policies?

Yes. Prince William Water can support development activity as envisioned in the Prince William County Comprehensive Plan, including the latest Comprehensive Plan update which included the Digital Gateway, with capacity currently owned by Prince William Water supplemented with the purchase of additional capacity when needed from Fairfax Water. 

 As specific land use applications are submitted with the related water requirements, Prince William Water will continuously monitor and assess the availability of existing water supply and, if necessary, the required timing to purchase additional capacity from Fairfax Water. Any additional capacity from Fairfax Water would be withdrawn from the Potomac River. 

Meanwhile the ICPRB and Fairfax Water are working to build enough water storge in the system to meet the expected demand. There is a limit to how much water can be captured by reservoirs- it is not infinite.  As more treatment and watr storage needs to be installed in the Fairfax Water system, the cost of the Between 2022 and 2023 the cost of the water purchased (and a little less was purchased in 2023 than 2022) increase by 20%.