I think it's worth noting that the point isn't necessarily that the act of showering is unnecessary - but more that we should think about the chemicals we're using at such frequency, and whether they're necessary. Dermatologists say that shampooing more than about twice a week (for most people) is overkill and not only bad for the environment but not optimal for your hair.
A good steamy rinse might get done 90% of what we shower for. Maybe all that soap, shampoo, and conditioner 5 to 14 times a week is overkill.