It's helpful to put this number in context, although if the people you're talking to will do anything to avoid using the metric system, that becomes much more difficult.

Fortunately, now we have computers, which are great at unit conversion, so we can cut right through these feeble attempts at obfuscation. In non-medieval units, 10.9 billion gallons per year is 41.3 million cubic meters per year or 1.3 cubic meters per second. The river a few kilometers from me has a discharge of 22000 cubic meters per second (of fresh water dumped into the sea), so Google is the equivalent using 0.006% of the Rio de la Plata. Lake Superior contains 12070 cubic kilometers of water, which is 1.207 × 10¹³ cubic meters, also of fresh water, so Google's current use would dry up Lake Superior in only 290,000 years.

Google is mostly not very close to Lake Superior or the Rio de la Plata; a more relevant river might be the Sacramento River, which drains into the San Francisco Bay where Google was born, and it's much smaller than the Rio de la Plata. Specifically, its average discharge is 797m³/s, so Google is using 0.16% of the discharge of the Sacramento River. (But some of that is at datacenters far from California.)

https://en.wikipedia.org/wiki/Water_in_California#Agricultur... tells us that agriculture in California uses 34.1 million "acre feet" of water per year (Americans will do anything to avoid using the metric system, especially when they're trying to be sneaky). In non-medieval units, that's 42.1 billion cubic meters, and per year, it's 1330 cubic meters per second, almost exactly 1000 times Google's use. Of that, 18% (240 cubic meters per second) is spent on alfalfa, or was in 02014, anyway.

One major difference is that you need fresh water, like the water of the Sacramento River, to irrigate crops, but you can cool data centers with salt water from the ocean. It's less convenient, because there are a variety of annoying things that happen with biofouling and corrosion, but that's what you'd do if hyperscalers scaled up by another factor of 100× so that their water usage became large enough to be environmentally significant.

But that doesn't happen until they have 100× the computing power they have today. So anybody who tells you AI datacenters are a major water user is lying.