Methodology:

To determine the bath, shower and bidet hotspots around the world, we calculated the percentage of hotel bookings in each country, state and city that have showers, baths or bidets.

We used Booking.com to determine the total number of accommodations (hotels, apartments, holiday rentals, etc.) in each geography and then found the number of accommodations in each geography that have either baths, showers or bidets using Booking.com filters.

I was unable to find an option for "baths, showers, or bidet" in the booking.com filters, let alone options for each of those individually. So I'm not sure about the exact data used for this infographic.