Why you can hear the temperature of water

Original Article ↗ Hacker News Discussion ↗

Everyday perceptions of water temperature by sound

  • Many commenters report reliably hearing when water turns hot in showers, taps, kettles, or while making tea/coffee.
  • Some learned this in childhood (e.g., creek or sink sounds, being told to “listen for when it’s hot”).
  • Several are surprised others don’t consciously realize they can do this; others say they thought it was impossible until tested.

Proposed physical explanations

  • Viscosity difference between hot and cold water is widely cited (less viscous hot water → different splash dynamics).
  • Other suggested contributors:
    • Surface tension and bubble behavior.
    • Vapor pressure, steam noise, and humidity above the water.
    • Different flow rates/pressures of hot vs cold taps (though some argue pressure is usually the same).
    • Interaction with receiving surfaces (porcelain vs plastic vs metal).
  • Some suggest air properties (temperature, humidity, density, temperature inversions) also change propagation of sound.

Experiments, data, and tools

  • Links are shared to:
    • The original research preprint.
    • Supplementary datasets and raw audio.
    • A video/audio comparison and a YouTube explanation.
    • An Android “AI thermometer” app that guesses temperature from pour sound.
  • One commenter did spectral analysis of the NYT clips, noting distinct frequency “basslines” and more high-frequency “hiss” in hot water.

Broader implicit perception and related phenomena

  • Thread branches into other subtle, often subconscious discriminations:
    • Temperature-dependent sounds of snow, ice, creeks, and church bells.
    • Perception of frame rates and motion blur on displays.
    • The McGurk effect and unconscious lip-reading.
    • Temperature and humidity effects on piano soundboards and tuning.
    • Smell of rain (petrichor), taste differences with temperature, and other fine sensory cues.
  • Several argue humans learn many such cues implicitly and then rationally deny having the ability.

Media and realism

  • Some note that films rarely get “cold” water or cold environments sounding right, since water and ambient sound are usually faked or recorded warm.