Ever have unreliable water because of service problems (widespread power outage or other). . . and would have found a simple, reliable method for purification/disinfection handy?
Oh, and lay in a supply of coffee filters and charcoal (for sediment and taste), if you want. As effective as most expensive methods, easier than boiling, especially if you’ve not *cough* prepared for an alternate method of cooking, and your primary method is interrupted.
Just have a few clear, 2-liter PET bottles handy, and some coffee filters, and you’re good to go for cleaning and disinfecting a source of suspect water.
Works also for camping. Does take six hours of sunlight, though.
Do note that you probably ought to have at least 3 days’ potable water safely stored at home, anyway, as well as a day’s supply in your car, just in case. Water for personal hygiene can be less stringently obtained and stored (tap water in safe storage vessels should be good enough for general washing), but drinking water–potable water–is more important for general emergency preparation, whether it be for storms, widespread power outages, or whatever.
Just sayin’.