The caveman had no way of knowing that, but think about it. He used something from Nature we don't even think about. The caveman inadvertantly discovered one of the secrets of water. Michelangelo and several Popes, drank the water from the Fuiggi Springs near Rome to prevent kidney stones. It's sacred powers were preserved by religious sects down through the centuries, as is evident by the many thousands of references in ancient manuscripts, including the Bible.
Water is a major factor in understanding universal phenomena, including the creation.
The oceans equilibrate the planet. The watery element supplies him with the physical body. The rain provides bread. The rivers orient his cities. The presence of water offers a blessing to his home and his workplace.