pqtb:
A "common" power surge through the incoming power lines may be blocked using surge arrestors (also called surge protectors) and/or voltage controllers. Of course if you have a device which is hard wired to your junction box, for instance the gas fired water heater you mention) you cannot insert a surge arrestor, at least not without re-wiring the device. I would advise doing this at the time of installation.
That being said, a common power surge is NOT an EMP event. The end result may be same, dead electronic/electric devices, but the protection needed is very different.
In the original video, it is noted that a lightening arrestor (NOT a surge arrestor) CANNOT act quickly enough to stop a true EMP induced voltage spike. I am reading conflicting reports on the use of lightening arrestors (also know as spark gaps). Again, a big factor is the use of longer conductors which may act as antenna elements for the EMP radiation (NO, not atomic radiation, an EMP is electromagnetic radiation).
I repeat my original statement, if you don't have full EMP proof containers, and use them, then the lucky might survive an EMP.
You may throw a lot of money at the problem, installing spark gaps, surge arrestors and voltage controllers into your power system. The question becomes, could that money be better spent buying multiple devices and EMP proof containers for those backup electronics?