During the cataclysms the ground is heaved and jerked, and any wells or piping will be shattered. In that the ground water is as likely to carry poisons as the surface, having filtered down from the surface, what looks like pure water from underground may be, again, a slow death. Ground water also is subject to contact with the lead heavy mantle, which most often does not make it all the way to the surface during eruptions. Distillation processes or recycling water known to be pure are two approaches likely to provide a steady supply of water. This may seem tedious to those so used to taking fresh, pure water for granted, but those who prepare for the times ahead will not find themselves suddenly without one of life's necessities.
Man dies without air in minutes, without water in days, and without food over weeks.