You are not solid. You cannot be grappled, grabbed, or pinned. You can flow through even the smallest cracks, although doing so may take a while. However, while you may be able to push things around with buffets of wind or currents of liquid, and even lift them, you cannot directly cause damage with any part of your body. You can cause normal ST based injury by picking things up and smashing them into something else.
Most fluid creatures have Injury Tolerance (diffuse), and take the Diffuse limitation on ST.