Board Thread:General Discussion/@comment-30827311-20170103044515/@comment-26484417-20170104124338

Demotivator wrote: Short answer: Rachel. That's more of a false answer. We know--from Baam's limited exposition--that it had taken a while before he first built that pile to reach the light, and then it had still taken quite some time before Rachel first entered the cave from beyond the light. All in all, he should have died of dehydration and maybe even starvation before Rachel first showed up, and that doesn't even account for the time before he started building that pile of which we know nothing.

In fact, the only answer that comes to mind, albeit speculative, is that Baam had been sustained by Shinsoo leaking from the Tower or something of the like.