Raft time?
Also, maybe it's just me, but cutting down the banana tree like that seems a bit short-sighted. Seems like you'd get more overall water by letting it live normally + just cutting holes in it and slowly gathering water, vs completely lopping off its leafy portion to make a stump that collects water.
Looking up the method he's talking about, I found a video claiming this method will generate water for 4 days, which in a normal survival situation might be enough, but if they've already been here for two weeks it seems like they shouldn't be using a strategy that'll require them to burn through potentially limited banana trees.