You could build a large filter yourself filled with layers of gravel, progressively finer sand and charcoal. As long as the water is not very heavily polluted with industrial waste etc. this kind of filter should work just fine. Boil the water before drinking to be on the safe side and you should be fine. The same goes for collecting water from the gutters. Rainwater is usually safer to drink and may not even require much filtering. Just don't collect any rainwater the first few minutes it starts to pour because it will contain all the dust and dirt on the roof and gutters.