Be an enterprising greenie and making your own water filter. You'll get fresh water for the least money down. At minimum, gather up some know-how now in case of a disaster that damages your water supply. (I live in Florida's Panhandle where the hurricanes have taught me this: it happens.)

As this Planet Green post explains, a purifying water filter is not something you have to purchase except for the sake of convenience. Nope. You can make your own water filter from fairly simple components. Including, um, cow manure and coffee grounds. Hmm... back to the drawing board for those of us without access to cow manure.

Another solution comes from this You Tube clip, which explains how to make a $3 water filter from PVC pipe. This one is cheap to make and it works to clear dirty water and make the water taste better. The down side: it doesn't filter pathogens, so water must receive chemical treatment to kill all the bugs. Mmm, chlorine.

If you need drinking water in quantity (say, for more than one person), you can consider a large in-ground filtration system. Green Trust tells you how to filter water using a large container like a 35 gallon drum. So drink up! On the science of water filtration, that is. Should disaster ever strike, you might be glad for the DIY knowledge.