Some embodiments of the invention provide a reverse osmosis water filtration system including a housing, a pre-filter cartridge, a reverse osmosis cartridge, and a post treatment cartridge. A medial water line transports a first portion of pretreated water from the pre-filter cartridge to the reverse osmosis cartridge. An unfiltered water line includes a flow restrictor and blend valve. The unfiltered water line is fluidly coupled between the medial water line and a blend water line. The blend water line receives filtered water at a first flowrate from the reverse osmosis cartridge and unfiltered water at a second flowrate from the blend valve. The first flowrate and the second flowrate are substantially equal to produce a consistent total dissolved solids value.