Friday, Jul 24, 2026 The claims desk. Receipts included. POWERED BY LENZ ↗
IsThis

SCIENCE

The Claim

At a fixed temperature, changing the total air pressure (lowering it by removing air or raising it by adding air) does not significantly change the maximum amount of water vapor that a given volume of space can contain, because the saturation vapor pressure of water is nearly the same.

Verified by Lenz ·

The Short Version

The claim is accurate in ordinary atmospheric conditions. At a fixed temperature, the saturation vapor pressure of water stays essentially the same even if total air pressure changes, so the saturation-limit amount of water vapor per unit volume also stays essentially the same. The main caveat is that this assumes normal, near-ideal gas behavior rather than extreme-pressure or exotic conditions.

Caveats

  • This describes the saturation limit, not the actual amount of water vapor present; relative humidity and current moisture content can still change.
  • The statement is strongest for ordinary atmospheric pressures and near-ideal gas behavior; extreme pressures can introduce non-ideal effects.
  • It assumes equilibrium with pure water; dissolved substances, strong curvature effects, or unusual mixtures can shift saturation behavior slightly.

The Receipts

  1. Table 1. Saturation (Temperature)

    NIST

  2. Accurate, simple equation for saturated vapour pressure over water and over ice

    Quarterly Journal of the Royal Meteorological Society

  3. Experimental Method for the Determination of the Saturation Vapor Pressure of Supercooled Argon in Nanopores

    PubMed Central

  4. 4.2: Saturation

    Geosciences LibreTexts

  5. 4.0: Vapor Pressure at Saturation

    LibreTexts / Practical Meteorology (Stull)

  6. Vapor pressure

    Encyclopaedia Britannica

  7. 4 WATER VAPOR (Practical Meteorology)

    University of British Columbia / EOAS

  8. Saturated Vapor Pressure - an overview

    ScienceDirect Topics

  9. Chapter 4: Water Vapor – Atmospheric Processes and Phenomena

    Pressbooks (University of Hawaiʻi)

  10. The many faces of water vapor: Relative humidity, dewpoint, mixing ratio

    Vaisala

+ 15 more sources — see the full list on Lenz

Filed Under

Saturation Vapor Pressurewater

More Fact Checks