Your going to need a very special filter (ceramic)to filter out nuclear contaminated water. Katadyn sells one (pricey to say the least) filters everything though. You will also need iodine tablets to flood your liver with. The water in your water heater comes from somewhere and will most likely be from a contaminated source. While we are on water you won't be taking showers so don't forget to carry a clothes pin for your nose from the stench that will be emanating from your loved ones after a few weeks without a shower. To get by you will need 1 gallon of water per day per person. To be safe you should have 2 gallons of water per person per day store up for at least 90 days to be safe, or access to a water supply that you can treat to drink safely. In other words those of you barricaded in that home of yours that have survived the people breaking in to take what you have. You will eventually have to come out of to get supplies and food and water! Amazing isn't it! Where there is a water supply is where the like minded community people you seek will be as well as the hordes of animals.