Generally, yes it’s a good idea. Ringtons would always recommend one.
Whether or not you need a water filter on your coffee machine depends on the quality of your tap water. If you live in an area with hard water, which contains a higher amount of minerals, then having a filter can help improve the taste of your coffee by removing some of these minerals. It’s best to do some research on the quality of water in your area before investing in a filter for your machine.
