H₂O · 18.015 g/mol · 104.5° bond angle

Water
moves.

It covers 71% of the planet, carries heat across oceans and pulls itself into droplets. Move across this surface to ripple it, then go down and pour out a bottle.

Open the bottle Read the numbers

Interactive · 500 ml

Press and hold the bottle for four seconds to twist the cap off, then watch it pour out.

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Physical properties · liquid at 1 atm

Six numbers that make water unusual

Hydrogen bonds hold water molecules together far more tightly than their small size suggests. These measured values are why that matters.

  • 997 kg/m³

    Density

    at 25 °C

    One litre weighs just under a kilogram, which is how the kilogram was first defined in 1795.

  • 3.98 °C

    Temperature of maximum density

    999.97 kg/m³

    Below this, water expands as it cools. Lakes freeze from the top down and fish survive the winter underneath.

  • 72.8 mN/m

    Surface tension

    at 20 °C

    The highest of any common liquid except mercury. It lets pond skaters stand and pulls spilled water into beads.

  • 4.184 J/(g·K)

    Specific heat

    liquid, at 25 °C

    About four times that of rock, so oceans warm and cool slowly and coastal climates stay mild.

  • 1.002 mPa·s

    Dynamic viscosity

    at 20 °C

    Honey is about ten thousand times thicker.

  • 100 °C

    Boiling point

    at 101.325 kPa

    Halve the pressure, as at about 5,500 m altitude, and it boils near 81 °C.

Earth's water budget · by volume

Where Earth's water sits

Almost all of it is salt water. Each bar below zooms into the highlighted slice of the one above, and the slice you drink from keeps getting smaller.

  1. All water on Earth

    1.386 billion km³

    • Oceans 96.5%
    • Saline groundwater & lakes 0.9%
    • Fresh water 2.5%

  2. Fresh water

    about 35 million km³

    • Ice caps, glaciers & permanent snow 68.7%
    • Groundwater 30.1%
    • Surface & other 1.2%

  3. Fresh surface & other water

    about 420,000 km³

    • Ground ice & permafrost 69.0%
    • Lakes 20.9%
    • Soil moisture 3.8%
    • Atmosphere, wetlands, rivers & living things 6.3%

Source: USGS Water Science School, after Gleick (1996). Rows may not sum to 100 because of rounding.

Residence time · logarithmic scale

How long a drop stays put

A molecule of water that evaporates today will fall again within about nine days. One that sinks into deep groundwater may not surface for ten thousand years. Each gridline is ten times the last.

  • Atmosphere9 days 9 days
  • Soil moisture1–2 months 1–2 months
  • Rivers2–6 months 2–6 months
  • Seasonal snow2–6 months 2–6 months
  • Glaciers20–100 years 20–100 years
  • Lakes50–100 years 50–100 years
  • Shallow groundwater100–200 years 100–200 years
  • Oceans3,200 years 3,200 years
  • Deep groundwater10,000 years 10,000 years

Typical values from hydrology texts, as tabulated in the water cycle literature (after PhysicalGeography.net and Wikipedia's water cycle article).