Bitcoin mines aren’t just energy-hungry; it turns out they’re thirsty, too. The water consumption tied to a single Bitcoin transaction, on average, could be enough to fill a small backyard pool, according to a new analysis. Bitcoin mines are essentially big data centers, which have become notorious for how much electricity and water they use.

According to the analysis published today in a commentary in the journal Cell Reports Sustainability, Bitcoin’s water footprint is growing. That’s an issue to watch as the price of Bitcoin recovers from a spiraling crypto winter.

The study was conducted by Alex de Vries, a PhD candidate at Vrije Universiteit Amsterdam, whose previous research has tracked cryptocurrencies’ electricity consumption and greenhouse gas emissions. Those issues have moved legislators to push for more oversight of crypto mines’ environmental impact. But until recently, most of that attention has been on whether energy-intensive cryptocurrencies like Bitcoin might throw off countries’ climate goals.

Bitcoin mining also has the potential to stress water resources in drought-prone areas. Miners use specialized computers to solve puzzles around the clock to validate transactions and earn Bitcoin in return. All that computing power burns through a lot of energy. And like other data centers, many crypto mines also use water in their cooling systems to keep machines from overheating.

“It’s hard to surprise me, given how I’ve already worked on this topic. I’m used to big numbers popping up. But then again, the numbers are still mind-blowing even to me every time I look at it,” de Vries told The Verge.

To conduct his analysis, de Vries estimated the direct water use from Bitcoin mines’ cooling systems. He added their indirect water consumption is associated with electricity generation since power plants also use water in cooling systems. He found that cryptocurrency mining used about 1,600 gigaliters of water in 2021, when Bitcoin peaked at over $65,000. That comes out to a small swimming pool’s worth of water (16,000 liters), on average, for each transaction. According to de Vries, it’s about 6.2 million times more water than a credit card swipe.

Of course, everything dipped in 2022 as Bitcoin plunged and mining slowed. But the price has climbed since last year, rising from less than $20,000 to around $38,000 today. The higher the price, the more incentive there is to ramp up mining. That’s why de Vries expects the cryptocurrency’s water consumption to rise to 2,300 gigaliters worldwide this year. In the US, the world’s biggest hub for Bitcoin mining, Bitcoin mining uses about as much annually as a city the size of Washington, DC.

These numbers are estimates based on the assumption that the Bitcoin mines run on water-dependent cooling systems typical in large data centers. However, some data centers and crypto mines use a different approach that keeps computers cool and reduces water consumption by immersing them in a non-conductive liquid.

Another way to get the cryptocurrency to use a fraction of the water and electricity it eats up now and slash greenhouse gas emissions is to eliminate the mining process altogether and find a new way to validate transactions. That’s what the following most extensive cryptocurrency network, Ethereum, accomplished last year.

If Bitcoin were to do something similar, “all the electricity consumption, associated water consumption, that will just disappear overnight. You know, we can make it happen,” de Vries said. “People still prefer to argue that the network isn’t as bad as we think it is, rather than trying to do something about it.”