That could be simply explained by principles of electrolysis.

When water is subjected to an electric current (from one node to another) and it contains other "heavier" elements like minerals, etc - these "contaminants" (not necessarily bad for consumption) decay and usually clumps into bigger particles which can be perceived with the clarity of the water.

If a "distilled" water is subjected to the same process, you'll notice that the same will not be observed, because, thru the distillation process, these heavier particles are removed.

The only thing you need to know when it comes to water potability is whether or not it contains organisms harmful to you (eg. E-coli, salmonella, etc). Given the strict regulations in the manufacture of bottled water in the Gulf, I doubt this could be a problem.