Water and earth are generally considered to be compatible elements. Water nurtures the earth and earth absorbs water. However, one challenge of this combination can be that more water is needed to nurture the earth. Further, the foundation represented by the prime triad lacks the air and fire element. Let's consider another example.
Water puts out fire and air evaporates water.
But don't stop there. Play with the images. Look for all the possibilities. Consider both the strengths that can be derived from such a combination as well as the potential challenges. Play around with the symbology.