One thing I suggest is that a new prepper take some classes from FEMA or the American Red Cross. Just about every government agency urges its own staff to prepare for disasters and emergencies in various ways. So, as a result of this knowledge, I started taking disaster survival classes from FEMA and the Red Cross.
Most groups urge you to have about a 30 day amount of food and medicines on hand and always ready. The idea is that most groups that urge preparation feel that eventually, within a couple of weeks, disaster response services will arrive with food and items for the area struck by the disaster. In other words, most agencies see disasters as a short-term issue rather than one that goes on for a really period of time like 6 months or more. To date, most of them have been correct BUT
I always plan ahead for a longer disaster/problem just to be safe. It doesn't hurt to be ready, just in case.
FEMA: Plan Ahead
Preparing and Getting Trained
As for water, I keep a small amount of bottled water around the home but I also plan to boil water or filter it over a long term amount of time. I don't think that one can realistically store enough water for all their needs so I plan on tapping into local reservoirs, streams and/or ponds as I need for longer events involving survival. So bleach, fire and purification tablets are all in my inventory for cleaning water.