The most official water costs $120k a gallon
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Vienna Standard Mean Ocean Water (VSMOW) costs $120,000 per gallon.
The article explains that isotopic variations in hydrogen and oxygen cause water's freezing point to vary slightly, necessitating a precise standard for metrology. In 1961, Harmon Craig proposed Standard Mean Ocean Water (SMOW), later named Vienna Standard Mean Ocean Water (VSMOW) after an IAEA meeting in Vienna. VSMOW is used to calibrate triple point cells, defining 0.01°C within millionths of a degree. A 5 ml ampoule costs $159, equating to $120,000 per gallon.
The Kelvin scale was redefined in 2019 using the Boltzmann constant, but VSMOW-based triple point cells remain the most accurate practical calibration method. Another standard, Standard Light Antarctic Precipitation (SLAP), is measured against VSMOW.
What commenters are saying
Commenters found the article enjoyable and compared VSMOW to other expensive reference materials from NIST, such as certified peanut butter ($2.44/g) and standard cigarettes ($508 each). One commenter noted that the value of NIST reference materials lies in the detailed measurement data, not the sample itself. A thread discussed the value of Kelvin over Celsius, with some preferring Fahrenheit for weather. A correction pointed out that modern Celsius is defined via Kelvin and the Boltzmann constant, not water's freezing and boiling points.