Water purifier, also known as water filter, is a small water treatment equipment that deeply purifies the water quality according to the requirements of water use. The water purifier usually refers to being used for home use.

Water purifiers can be divided into many types according to different purification principles and processes. Among them, RO reverse osmosis technology (used by countertop ro water filter dispenser)has the highest filtration accuracy (filtration accuracy in 0.0001 microns), because the pore size of the reverse osmosis membrane is five millionths of a hair, only water molecules and dissolved oxygen are allowed to pass through, and all impurities contained in the water such as pesticides, bacteria, viruses, heavy metals and other harmful substances are almost all intercepted and excluded.

Reverse osmosis is a membrane separation technology with the help of the function of selecting the permeable (semi-permeable) membrane to push the pressure, when the pressure added in the system is greater than the osmotic pressure of the inlet water solution, the water molecules continue to pass through the membrane, flow into the central tube through the water-producing runner, and then flow out of the water at one end, such as ions, organic matter, bacteria, viruses, etc., are intercepted on the inlet side of the membrane, and then flow out at the outlet end of the concentrated water, so as to achieve the purpose of separation and purification.

In addition to reverse osmosis technology, there are many other filtration technologies: nanofiltration (filtration accuracy between 0.001-0.0001 microns), ultrafiltration membrane (filtration accuracy between 0.1-0.01 microns), fine filtration (filtration accuracy of less than 0.1 microns, such as ceramic filtration PP cotton filtration, etc.). The application of deep water purification technology in the field of drinking water makes the phenomenon of "water and soil dissatisfaction" soon become history. Effectively solve the endemic diseases caused by excessive harmful minerals in groundwater in many places.

The water purifier has wastewater because it has too many substances to take away, it must have wastewater, if there is no wastewater, those substances that cannot be seen by the naked eye will remain on the RO film, in the long run, then the effect of the RO membrane will also be lost, and at that time, it is no longer clean water, but water that is no different from the original.