You really want to avoid spraying directly into their mouth, even when they open up and make it so tempting. You want to let them drink from water collected on leaves for misting, some will even drink by opening their mouths repeatedly during the misting, drinking the water that is gathering around their mouths... This is the natural way... Spraying water with force directly into their mouths risks getting water down the wrong pipe, and possibly drowning your cham. This is dangerous as it is not how they are designed to drink, it is incredibly unnatural. Imagine how easy it would be to choke if you were having your drinking water sprayed into your mouth instead of being allowed to sip. I would recommend allowing your cham to learn how to drink on their own... I typically mist mine until I see them start to open up to drink. Then I stop and let them drink what they want from the leaves. If you have a Cham that is refusing to drink and becoming dehydrated this is when you must consider more manual ways of getting water into their system.
~Joe