I suspect that isn't true, but it is an interesting question. There is a lot of water on the planet, some of it spends long periods locked up out of reach of drink ability.

I would guess that at most water has been drunk multiple times, but that there is some miniscule a fraction that moved between icecap, permafrost and deep water table and has avoided being consumed by an animal since it arrived on earth.

I would be interested to read a mathematical estimate of how many 9s of water on earth has been drunk at some point.

Somewhat related XKCD What if: https://what-if.xkcd.com/74/

drunk by a human or drunk at all? I'd suspect that not all water has been drunk at all, but lets cover the human part.

Lets say the average human drinks 3 liters per day and lives 80 years (3 * 365 * 80 ) = 87,600 liters per human.

there have been about 100 billion humans so 100 b * 87600 =8,760,000,000,000,000 liters have been drunk.

there are about this many liters in Earths 5 oceans (source google search): 1,400,000,000,000,000,000,000

Assuming no one has ever drank the same amount of water before, 8,760,000,000,000,000 < 1,400,000,000,000,000,000,000

It sounds fairly certain that not all water has been drunk by a human, even if my math is way off