Claims for virus removal cannot be substantiated well. Some filters incorporate iodine resin or charcoal filter. Most of these filters will take the chlorine and some metals out of water to make it taste better but do not filter out the bacteria. Do not rely on this type of water if you are at all uncertain of the quality of the water. They are the best way to ensure that water is okay to drink and won't make you sick.
Unclean water poses a risk for gastrointestinal and other problems.
If you are concerned about having enough water, one idea is to get one of those above ground type swimming pools you can get at places like Wal-Mart or Kmart. In fact, they are probably on sale now that it's fall. Those large pools probably hold about 2-3 thousand gallons of water and all you need to do is treat them with chlorine and cover with a tarp. You could also use roof water catchments and drain into a kiddy swimming pool. Now it may seem that the cheapest way to treat water is to boil it for half an hour, but remember that boiling water takes fuel and you may be in a position where you want to conserve your fuel as much as possible.