A standard water filter should be replaced every 2 to 6 months. Filters in wells may only need to be replaced every two months. Every 3-6 months, carbon filters must be replaced. It’s also a good idea to stick to the lower end of this spectrum.
If you wait 6 months, algae and mold may form, therefore it’s best to act sooner rather than later. These figures, however, might fluctuate greatly depending on the conditions. A family of seven in a big home will need more regular filter replacements than a couple living alone.