"IZU is the masculine, stern aspect that gives form to the universe; MIZU is the feminine, gentle aspect that gives it function. IZU, associated with Izanagi, is the Father, MIZU, accociated with Izanami, is the Mother. IZU sanctions and corrrects, MIZU offers love and goodness. The two aspects interect to shape the Cross of Aiki, which sustains the world. Morihei stated that this cross of IZU-MIZU was the basis of Aikido."
from "The Essence of Aikido", Ueshiba/Stevens, pg. 47.
Hope that helps,