Sealing mast

During my first capsize in my 1999 Nacra I-20, my carbon mast wanted to sink. Managed to keep it up, but close to turtling. I removed the base cap and planned to fill the mast with water to see if I have leaks. Found it filled with expanded foam. Can I still add water from a garden hose to look for leaks? Or will the water just make the foam soggy?