When you ask ChatGPT a question, you’re not just using electricity, you’re using water too. But just how much? According to OpenAI CEO Sam Altman, it’s only 0.32 milliliters per prompt, about one-fifteenth of a teaspoon. That’s surprisingly small, but it adds up fast.
Why Does ChatGPT Use Water?
The water isn’t used by the AI itself, it’s needed to cool the servers in massive data centers that run tools like ChatGPT. These servers generate a lot of heat while processing your prompts, and water is often used in cooling systems to keep them from overheating.
Altman shared this figure in a June 2025 blog post, noting the estimate reflects direct water usage, specifically for server cooling. But not everyone agrees with that number.
Earlier Studies Reported Much Higher Usage
Previous studies in 2024 conducted in collaboration with The Washington Post and the University of California, Riverside, claimed that generating a 100-word email using ChatGPT-4 could require up to 519 milliliters of water. These earlier estimates appear to include both direct and indirect water usage, such as the water used in electricity generation.
Academic research further supports the idea that total water usage can vary widely depending on data center location and infrastructure. A study published on arXiv in 2023 found that the amount of water used per prompt ranged from around 7 milliliters in Texas to over 47 milliliters in Washington state. This variation is largely due to regional differences in cooling systems and energy sources.
Despite the low per-prompt figure provided by OpenAI, the cumulative environmental impact of ChatGPT could be substantial. With more than 400 million weekly users and billions of queries processed each day, even a small amount of water per prompt adds up to a significant total. While OpenAI and other tech companies have committed to sustainability goals, including becoming water-positive by 2030, transparency around actual usage remains limited.
As of July 28, 2025, the most current and direct estimate from OpenAI suggests ChatGPT uses about 0.32 milliliters of water per prompt, focusing on direct cooling usage. However, earlier studies indicate higher figures (e.g., 16.9 ml per request on average in the U.S., including indirect usage), reflecting the complexity of environmental impact assessments.
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- Sam Altman’s Blog Post – States ChatGPT uses ~0.32 ml of water per prompt (June 2025).
- TechRadar Article – Discusses Altman’s water usage claims for ChatGPT (June 2025).
- The Washington Post Article – Estimates 519 ml for a 100-word email with ChatGPT-4 (September 2024).
- TechRepublic Article – Covers higher water usage estimates, including indirect usage (2024).
- TechTimes Article – Supports Altman’s 0.32 ml per prompt figure (June 2025).
- Fello AI Article – Estimates ~1.67 ml per prompt based on 500 ml for 300 queries (February 2025).
- Reuters Article – Notes ChatGPT’s 400 million weekly users, contextualizing scale (February 2025).
- Microsoft’s Sustainability Report – Details efforts toward waterless cooling for AI data centers (2024).
- Google’s Environmental Report – Discusses water-positive goals relevant to AI data centers (2024).
- AP News Article – Highlights lack of transparency in AI water usage, focusing on Iowa data centers (2024).
