SL-1 was an Army reactor, so I would say it doesn't count. I'd also not count the USS Thresher or the USS Scorpion, since reactor accidents weren't the reason those sank.

Relative to how many people die every year from wood and coal smoke? I would say it doesn't count in a relative sense.

Most civil reactors are next to lakes or rivers so it seems like they should have plenty of water. Is it a matter of civil reactors using smaller[cheaper] plumbing and pumps? My intuition is that Naval reactors are built to be very responsive because that's useful for naval applications, but civil reactors aren't built like that because that ability has less relative value for civil reactors.