This term is so relative. The first thing someone considering a hole house water filtration system is the condition of the water. A good place to start is the local college extension service. Most university and community colleges have extension service were residents can have water and soil tested. Also check your local water department for water testing services.

Once your water has been tested you will receive a report listing any minerals, metals sediments Etc. Deciphering a water report can be overwhelming to someone with no knowledge in the field. You water department can help with this aswell. Once you determine what needs to be removed from the water you then

Consumer Reports say the following about

Best for inexpensively removing sediment, rust, and for some, chlorine, from household water. Long cartridge lifetime.

But most not designed to, and won’t effectively remove, most other contaminants, including cysts, metals, and VOCs. Whole-house systems require professional installation

Best for removing a wide range of contaminants, including dissolved solids, and is the only filter certified to remove arsenic.

But requires plumbing modifications and must be periodically sanitized with bleach. Is extremely slow and creates 3 to 5 gallons of waste water for every gallon filtered. Takes up cabinet space