What is a Waterfall Word™?

_{This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.}

If a word conforms to a special rule, I call it a Waterfall Word™.

Use the following examples below to find the rule.

And, if you want to analyze, here is a CSV version:

Waterfall Words™,Not Waterfall Words™

ANTACID,MEDICINE
BEAMED,SMILED
COSMOS,UNIVERSE
CRAMPS,PAIN
MEANT,IMPLIED
MEANY,BULLY
PANEL,FRAME
RABID,SICK
RAMPANT,WILD
SCRAM,GET

TACOS,CHIPS
TAXES,FINES
VISCUS,VISCERA
WAVY,BUMPY

Answer

Waterfall words run down the keyboard (using qwerty layout), so a letter from the top row is followed by one from the middle row, then one from the bottom row, looping as needed.