Yes, water filters can be outside. There are a few things to consider when determining if a water filter can be placed outside. The first is the climate. If the area experiences freezing temperatures, the filter will need to be protected from the elements or brought inside. The second consideration is sunlight exposure. If the filter is exposed to direct sunlight, it will degrade faster. Finally, if the filter is in an area with high dust levels, it may need to be cleaned more often.