The potential for radioactivity would be my biggest concern, as well. Also, there is a chance of EMP taking out things like well pumps, generators, etc.
NOT a large chance, I don't think...but who really knows.
We have an artesian well which runs 15 gallons a minute of wonderful water. We've set it up so a few minutes work will divert the overflow into the basement... where we can then divert it to a drain that runs to the drainage system around the house. "Just in case", of course, we can't safely go outside and draw water from the well with buckets.
But... I still have enough water stored for the 11 people I would expect to be here in a major SHTF scenario. Essentially, one 4' X 18" 5 shelf unit full of 2 quart juice bottles. Yeah... it seems over the top at times.
But oddly enough, it's one of the preps we've used more than almost any other... when the well pump went bad and we had to work on it.. grabbed a bottle of water and set them at every sink. When the power goes off, we don't want to run the big generator (it runs the whole farm) all the time. So once chores are done and the milk is cool... no water in the house. Except for the convenience of fresh bottles available any time someone wants a drink.
With your preps, you probably don't need to store a ton... but maybe 5 gallons per person (enough for 10 days of drinking water if you were very careful) wouldn't be a bad idea.
Summerthyme