Here’s climbing guide Stephen Koch on how he likes to carry water when he’s climbing:
“I like carrying water off of my harness to lower my center of gravity, especially during steep climbing. If the bottle leaks from my harness, my jacket or sleeping bag don’t get wet! Another reason I like drinking out of a bottle is so that I know how much water is left! It can be frustrating while using a hydration bladder to be half way up a climb thinking I have plenty of water left only to discover I am sucking the last of it down without knowing it.”
Here’s his video demonstrating how he makes one of these.