The charcoal looking stuff is most likely peat that was dislodged during the recent storm. I've picked up some of it lately to verify, and it isn't tar balls from the oil spill. Alabama did have some more tar balls wash up, and according to the reports it was pretty much in the same condition as when fresh, which is more squishy and browner than the peat.
We have always had this peat here. It's harmless. But it's covered up a good bit of the time, so you have to be here a while to see it often enough to get familiar with the difference between it and tar balls.
I hope whatever kind of bottled water you are buying is not distilled, which has all the minerals removed. The minerals are essential for health. And also make sure it isn't crap like Dasani, which is tap water filtered and with some minerals added.