https://www.theregister.co.uk/2018/05/30/para_ortho_water_separation/

Boffins have, for the first time, managed to separate water into its two isomeric forms to test how they react to stuff, according to a paper published in Nature Communications on Tuesday.

You may or may not know that each water molecule exists in one of two slightly different structures: para-water and ortho-water. Both have two hydrogen atoms bonded to a single oxygen atom. In ortho-water, the nuclear spins of the hydrogen atoms, which point up or down, are aligned in the same direction. In para-water, however, the spins are in opposite direction to one another. In chemistry, these two forms are known as isomers.