I’ve never heard anybody claim “net” dehydration. Have you? You might be misinterpreting.
Generally, I think the claim is it is more diuretic than water or other non-caffeinated liquids.
After brief research, caffeine is a Xanthine-class diuretic than inhibits reabsorbtion of Na+. Wow, Wikipedia says the diuretic effect is only “when intitially consumed in large quantities” but “this effect disappears with chronic consumption.” 😂
