I've been paying attention to this situation for a few years now. It seems to me that one of the biggest threats to surviving an EMP is loss of water. Our water is delivered largely by gravity. But the pressure head that delivers the water comes from water being pumped into storage tanks that are elevated high above the end user. The water only gets to those tanks via electric motors in most cases. So in the case of an EMP we'll have a few days of water pressure...and then nothing. Water is one of the hardest things to store in bulk.