NVIDIA's 45C inlet water lets a data center run with no evaporation
Coolant goes in at 45C, comes out near 55C, and never boils off into the sky. In a favorable climate, dry radiators alone shed the heat and the water bill drops toward zero.
Rubin-generation racks go fully liquid: every chip and switch sits on a cold plate, no fans, with 75% water and 25% glycol in a sealed loop. A 50MW site is pitched at over $4M a year saved on cooling and water.
Practitioners say the catch is climate. You need outside air below about 37C to guarantee a 45C outlet, so most sites still keep cooling towers for the hot days.
And the bigger water sink stays untouched: power generation, not the building, is where most of a data center's water actually goes.
Cooling without boiling water away
NVIDIA's pitch for its Rubin generation is 100% liquid cooling: every processor and networking component sits on a cold plate, fans gone, in a closed loop of 75% water and 25% propylene glycol. Coolant enters at 45C and leaves around 55C. In a favorable climate, dry coolers, outdoor radiator coils, shed that heat to the air with no evaporative tower, which is what drops water use toward zero. The framing number: a traditional tower consumes roughly 2.6 million gallons per megawatt per year. Cooling has historically eaten up to 40% of a data center's electricity, and the company claims a 50-megawatt site saves over $4 million a year.
The real change from earlier “liquid-cooled” racks is coverage. Those were hybrid: GPUs and CPUs got cold plates while everything else stayed on finned heatsinks in moving air. Rubin redesigned the rest of the board for liquid, which is what lets fans disappear.
Practitioners say the asterisk is the local weather
The headline number assumes a climate that cooperates, and the people who design these rooms said so. One spelled out the temperature ceiling and why the towers don't actually vanish.
“You'd need outdoor air to be below ~37°C to guarantee 45°C water outlet temperature. In most locations you still need cooling towers or compressors some of the time…” — an engineer sizing a London-area build
A hobbyist running the same idea at home confirmed it isn't exotic, just productized.
“I am pretty much doing the same but running the coolant at 40 deg C instead of 45 as my pumps are rated for 45 C max temp.” — a CTO with a Blackwell waterblock build
The sharper rebuttal was that the whole “near-zero water” frame measures the wrong tank.
“The major source of water use in datacenters, by far, is the water used in power generation… the savings are almost certainly under about 20%…” — a CMU professor and ex-Google Brain engineer
Others were more blunt that the announcement targets a complaint, not a constraint.
“It's a response to the FUD that is water usage in data centers… Data centers used about 66 billion liters 2023… Golf courses used 2 trillion liters in 2020.” — a commenter citing the eScholarship figures
The more interesting downstream idea wasn't dumping the 55C output but selling it: 45C is low for district heating but not unworkable, which turns a noisy neighbor into a heat supplier for the town next door.
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