This listing is a 6-stage RO+DI Reverse Osmosis + Deionization water purification system. It is designed to tap into your water supply line under-the-sink or to a garden hose valve. Once it is connected to water supply with above 45 psi input pressure, the system is able to purify the tap water into ultrapure water at a rate of 120 gallons per day or about 5 gallons per hour. For example, if the water quality of tap water is 300ppm, after 4th stage RO membrane filter, the TDS reading will be reduced to about 25ppm, then the 5th & 6th stage DI filters would further reduce the TDS to 5ppm to 0 ppm. The filters used in the system are, 1st stage sediment filter, 2nd & 3rd stage carbon filter, 4th stage TFC-150 RO membrane, 5th & 6th stage color changing DI filters. DI resin changes to black color when it is exhausted. The system includes all filters, tubing, under-the-sink adapter and installation hardware, and extra garden hose adapter, and instruction, and free tech support in USA. This system is designed and assembled in Santa Ana, CA, USA. We have been making RO systems for 23+ years. They systems we built are reliable and guaranteed to perform.