Back in 2016, geologists from the University of Toronto announced they had discovered water at the bottom of an old mine in Canada that was 2 billion years old. The claim was based on the presence of dissolved salts and noble gases, which suggests how long the water had been isolated.
However, the water itself must be at least 2 billion years old but this work did not reveal when it formed. So how old is this water or indeed, any of the stuff we drink?
Today we get an answer thanks to Cecilia Ceccarelli at the Université Grenoble Alpes in France and Fujun Du at the Purple Mountain Observatory in China, who have studied the way water forms and where most of it on Earth is likely to have come from.
Their conclusion is that most of the water we drink formed during the early formation of the Solar System some 4.5 billion years ago. In other words, it is older than Earth itself.
How they arrived at the number involves some in-depth analysis of the formation of the solar system and some chemistry. You can find all the details here: