If you visit a bar after a tsunami, you’ll be hanging out in shallow water. After a tsunami, you want to relax with a drink at the bar. Unfortunately, tsunamis cause floods, and the bar floor is immersed in shallow water.
What beer are you drinking at this bar while standing in shallow water? You’re drinking Asahi (あさ), the beer of the salaryman. Asahi is super dry, so it takes your attention away from the shallow water a bit.