A mind (spirit) like
water. The perfect calm which the mind or spirit can find,
producing a non-aggressive state and a feeling of "passive"
resistance. Whoever possesses Mizu-no-Kokoro is thus sensitive to
all impressions, just as water is sensitive to the slightest breath of
wind, and his or her Ki is in harmony with all beings.
From A Dictionary of the
Martial Arts by Louis Frederic, Charles E. Tuttle Company, Inc., Boston, 1998.