The WGB21B is a great "point of entry" filtration system and an excellent alternative to the larger WGB22B (4.5"X20") for smaller homes or where limited space may be a concern. Unlike "point of use" systems the WGB21B will filter water directly from your source. This means that water from every outlet in your home will have passed through this filter, providing up to 50,000 gallons of clean water for the entire family.