Water has been used as a metaphor for the expression of philosophical, and martial art concepts for many years. Water is a seemingly simple element, yet it is one of the key building blocks of life itself. A deeper examination of its properties reveals its unique ability to adapt to changing circumstances. Unobstructed, water flows in a continuous and steady stream - as should the energy of the martial artist. When a rock is placed in its path, the water adjusts its course to flow around, over, or under the obstacle. In a similar fashion, a Hapkido practitioner does not seek to force his attack or defense against the power and momentum of the aggressor. Rather, he or she "fluidly" adjusts their own position and adapts to the attacker's movement and rhythm. While adjusting to the speed or angle of an assault, the primary objective is to harmonize with the aggressor's movements, using the opponent's energy to counterattack. With minimal additional effort the defender is able to re-direct the attacker's power against them. Hapkido instruction emphasizes the ability to adapt and respond to any given situation. Moreover, when technique flows effortlessly through the practitioner, this is an indication that he has taken Hapkido and made it his own.
The water principle is an essential philosophical concept within Hapkido. Water accepts a foreign object even as it sacrifices a portion of its own space. Similarly, a student of Hapkido learns to share his or her time and energy with others in and outside of the studio. One's own ability and character development are enhanced by supporting others and contributing to their progress and well-being. The martial artist carries a deep obligation to the society in which he lives, to protect and defend those in need.