The water efficiency grade of the water purifier reflects the net water output of the water purifier. According to the national standard GB349 14-20 17 "Water Efficiency Limits and Water Efficiency Grades of Reverse Osmosis Water Purifiers", the water efficiency grades of water purifiers are divided into five grades according to the net water output, and those higher than Grade 2 (including Grade 2) are water-saving products. The net water yield refers to the ratio of the total purified water to the total water intake after the water purifier is purified by the reverse osmosis system under the experimental conditions specified by the standard without reducing the service life of the reverse osmosis membrane.