The water coming from the main city line isn’t always optimal. It often has a surplus of minerals such as calcium that can affect the pipes and fixtures over time. Some people may also have sensitivities to the water such that undesirable elements must be filtered out before they can use it.
Using a filter for the whole house is ideal as all sources will then provide clean and conditioned water. You can be confident drinking from the tap and using the heater. The appliances and fixtures will no longer suffer from mineral build-up. The taste will be much better.
Find the best whole house water filter that you can afford. It can be a significant investment but you are probably going to love the results. Not only will the quality of your water be better, you can save money from not needing plumbing repairs.