Use a hollow steel ball with a threaded steel  plug.   Immerse in water to fill.  Thread plug, close tightly.   Immerse in liquid nitrogen behind a strong shield.  Water will shortly freeze, but cannot expand.  Eventually, the container will explode due to increased pressure.

On Wed, Dec 1, 2021 at 6:33 AM, Karl
<gmkarl@gmail.com> wrote:
I'm not sure how to build a bomb out of water.