Veiled chameleons live in country where free water is scarce and rain is seasonal, but where nights are cool enough for heavy dew and mist. The casque, a laterally compressed bony crest that can exceed five centimetres in a large male, presents a broad vertical surface for condensation. Water beading on it runs down grooves toward the snout and is licked up.
The behaviour is familiar to keepers, who find that chameleons will not drink from a standing bowl but will drink readily from misted foliage and from droplets running off their own heads. It reflects a general chameleon reliance on moving droplets rather than pooled water, which is why captive husbandry uses misting and drippers.
The casque's other functions are clearer: it is sexually dimorphic and grows with maturity, so display and species recognition are involved. How much of the animal's daily water budget the casque actually delivers under field conditions has not, as far as published work goes, been quantified, and the drinking function should be treated as well-observed rather than measured.