The Drop icon on the LCD screen shows total dissolved solids (TDS), i.e. liquid purity in PPM (parts per million). Use the following criteria for reference:
Blue light: 0-100 PPM (no solids) – high purity
Green light: 100-350 PPM (some solids) - average purity
Red light: 350 PPM and up (exceeds the permissible solids level)*
*Coffee, tea, and juice typically contain dispersed particles, thus the Drop will turn red.