No, it's tap water. And I sure as hell hope it isn't the water, since I drink the same.
I doubt it's that, the other dog has been epileptic for about a year, but he's been on medication and hasn't had a seizure for as long as I can remember clearly. Where'd you hear about the groundwater contamination? I'd like to look into that.
My cousin lives in that area, and both his dogs had seizures (they were both from the same line of dogs, a generation apart, but my dog was also from the same litter as the younger one and hasn't had any such problems), with the younger one dying of cancer last year. According to them, the water that comes out of the tap is blue and smells like sulfur, and going off what they said they believed the groundwater to have been contaminated by a specific pesticide (or fertilizer, I can't recall which) that was in use at a farm that had been located nearby. They stopped giving the dogs the tap water after a while, but have remarked that they've heard that an unusually large number of dogs in the area suffer from the same problems.
I can't confirm the veracity of any of this, mind you, aside from the dogs having seizures and the one dying of cancer last year, nor do I have more details than that. It was just the first thing that popped into my head when I read your post, and if your tapwater doesn't come from a well, it's probably something else. Most of the time seizures in dogs are fairly benign, and easily treatable, as I understand it.