This is one of the best sales pitches for the metric system that I've ever seen.
It's equally silly to try to convey the size of a cubic mile of water in gallons, just as much as it is to convey the size of a cubic kilometer in liters. The numbers are just round in the latter case.
In other words, both:
1,101,117,147,000
1,000,000,000,000
Edit: now a trillion, that's getting beyond comprehension. Just multiply each side by 10.
Edit edit: that "1 billion" would make for a good conversation piece. Or, easier, a container with 1 billion small grains in it.
You're right that large numbers are hard to comprehend, but being able to summarise them and convert to other measures easily helps convey meaningful information.
Saying you want to process a billion tonnes of something is immediately grokable as vastly different to wanting to process a million tonnes.
Being able to immediately convert that into a conversation about processing a trillion litres vs a billion litres is similarly valuable.
If I can process 1 tonne of water per unit time, then I know that the cubic km will take 1000 times longer than a billion litres / million tonnes.
> are equally meaninglessly
> large to any lay reader.
It contains however many liters of water are in that cubic kilometer after you subtract everything else in the ocean, it'll be close to a trillion liters, but not quite.
Of course the article may be using "water" in the loose sense.
But if it's not the metric version would implicitly provide you with an easily inferred percentage of how much of a cubic kilometer of ocean is made up of other stuff.
Whereas in imperial units you won't know that at a glance, you'll need to either repeat the calculation, or memorize various conversions.