Refresh your understanding of personal water consumption by diving into the subject of handwashing in people’s day-to-day lives.

Fermi problems require you to make a quick estimate of a quantity
that seems difficult or impossible to determine precisely. They
were named after Enrico Fermi, the Italian physicist who used this
problem solving method to predict how atoms would work long
before scientists had the technology to actually see atoms. Fermi
problems emphasize the process of solving problems over getting
the exact answer.