[el ess A]

While the "fire hose" scene was a bit over the top and somewhat unrealistic (even for an unrealistic zombie apocalypse show), the main reasoning behind it was to depict that Eugene was coming out of his timidness and hiding behind others to take the fight to the walkers.

The idea is that rotting walkers' heads were spongy and could easily be blasted apart, and thusly killed, by the water pressure. The water pressure was deliberately cut back so as not to hurt the actors in the zombie get-up. To note, in reality, those deck guns can shoot over many a building.

But telling Abraham that he was still smarter than him while Abraham was in his wild state of mind certainly wasn't the smartest thing to do.