Globally in 2018 there are 370 billion credit card transactions, divided by 6 million for swimming pool comes to 62,000 swimming pools worth of water for global credit card transactions.
Or 170 swimming pools a day
Or seven swimming pools an hour.
Bitcoin is targeting 10 minutes per block on average, so that's 144 blocks per day or six swimming pools per hour.
I don't really have a point with this math, just that if an article is going to make a colorful analogy, they should take it all the way so we can have comparables