First of all, lot's of people WILL survive a nuclear bomb explosion. If they survive the blast and heat, that is. Most of the heaviest particles (alpha & beta) have very short half-lives. If you're too close to ground zero, the x-rays and gamma rays are pretty bad and you well could die or get severe radiation sickness, but many dozens of miles away from the blast zone there won't be a big exposure. Because the most radioactive particles are heavy, they should fall downwind of ground zero with 25-40 miles. Outside of this zone one can protect themselves by wearing heavy clothing, staying indoors with the windows shut, and and eating food that's protected (cans, boxes, shrink-wrap) for a few weeks. Water is what you need to have IN THE HOUSE BEFORE it can be contaminated. If you don't have any, water from COVERED sources will probably be ok.
I say this as a VERY WELL trained USAF Disaster Preparedness NCO who dealt with this for a number of years. Also, I'm a red-zoner, where a terrorist attack by nuclear means is very unlikely. In the even of a nuclear attack, I will house bona-fide FReepers from the Blue zone at no charge. No DEMOCRATS! :->
Those who prepared for a possible Y2K event were mocked and ridiculed by many. Americans generally think serious preparation for such things as nuclear attack is only for nutcases and extremists.
A lot of people will die from a nuclear attack and it will be because of their own foolishness and lack of preparation. Americans have the ability to prepare themselves for disaster but make the choice not to do anything. The government has fooled the people into believing the government will protect them from whatever comes. The government has already proven it can no longer even control our borders. We are on our own to survive. A few will. Many won't.
Dont forget your water heater in you home is a great storage supply of water.