The Invisible Trillion

The Water Question, Honestly

Why the Answer Depends Almost Entirely on Where You’re Standing

If you spend any time on the internet, you have probably seen some version of this claim: training GPT-4 used enough water to fill a swimming pool. Every ChatGPT query you send drinks a bottle of water. Data centers are draining the planet.

Some of that is roughly right. Some of it is exaggerated by a factor of ten. Some of it is technically true in ways that turn out, when you look closely, to mean almost nothing. And some of it is genuinely concerning, but for reasons that are very different from what most people mean when they repeat it.

This chapter is going to walk through the actual water story — where water is used, why, how much, and in which places it actually matters. The honest summary, which I’ll expand on below, is this: the water problem with chips and data centers is real, but it is overwhelmingly a local problem, not a global one, and the local problems are concentrated in a small number of places that most of the scary statistics don’t distinguish.

How Water Gets Used, and Where

There are two completely different ways chips and data centers use water, and it’s important to keep them straight because the stories are very different.

The fab uses water to make the chip. A chip fabrication plant — the factory from Chapter 3 — uses enormous amounts of ultrapure water to rinse wafers between processing steps. Ultrapure water is regular water that has been filtered to the point where it is actually slightly toxic to drink (it leaches minerals out of your body). Fabs use this water because chips are so small that even trace contaminants in ordinary water would ruin them.

A single large fab uses somewhere between 5 million and 20 million gallons of water per day. TSMC, which makes most of the world’s most advanced chips, uses about 150,000 metric tons of water per day across its facilities in Taiwan. That is a real and large number.

The data center uses water to stay cool. A big data center generates enormous amounts of heat — tens of megawatts of it, which is roughly the heat output of a small town. That heat has to go somewhere, and the cheapest, most efficient way to get rid of it is evaporative cooling: spray water on a surface, let the water evaporate, and the evaporation carries away the heat.

A big data center using evaporative cooling can use 1 to 5 million gallons of water per day. The amount varies enormously depending on how the data center is built.

These two uses — fabs and data centers — add up to, globally, something like 0.1–0.2% of total human water use. That’s a real number. It’s not zero. But it’s also much, much less than people think.

For comparison:

Agriculture: about 70% of all human water use, globally.
Livestock (just the animals, not including feed): about 30% of agricultural water, or 20% of total.
One pound of beef: about 1,800 gallons of embedded water.
One cotton T-shirt: about 700 gallons.
One pair of jeans: about 2,000 gallons.
One almond: about 1.1 gallons.
One American golf course: about 500,000 gallons of water a day.
One American family, residential use: about 300 gallons a day.

Put another way: the entire global chip and data center industry uses less water per year than American residential lawn watering. Not lawn care in total — just the watering of grass.

This is the kind of context that almost never makes it into the viral posts, and it matters.

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