If you have a whole-house water filter, make sure you change the filter every 3 months, or as recommended by the manufacturer. Changing the filter is important to keeping your water clean and healthy. If you leave a dirty water filter in for too long, bacteria can build up and enter your water supply. This also applies to filters for point-of-use filters such as reverse osmosis filters. Keep your filters clean and up to date and you'll avoid the nasty gastrointestinal problems that can result from a contaminated water supply.