Treatments pretty much come down to chemicals, heat, UV exposure, and filtration. Filtration, ideally through activated carbon, is the only one that is going to be reliable against the potentially toxic man-made chemicals common in urban and suburban environments.

I'm not sure what storing a quart/liter of water for a time is such an issue. At about two pounds I can't imagine how it could be an issue. Five gallons, at roughly eight pounds per gallon, forty pounds, would be prohibitively heavy and fairly bulky. But a liter or two ... not so much.