Every scuba diver has a plastic plate and pencil for communicating anything more complicated than what ordinary hand signs will do...

Alas, I fear that the very presence of such a notepad would eliminate whatever feature it is of showers that make them such frequent idea-generators.

You need a good pen too, since most won't write underwater. Divers use the same sorts of space pens that NASA does, or similar designs that take the same ink cartridges. They can write in boiling water or in Antarctic temperatures, or even upside down. I have one, but have not tested these claims yet.

As a side note, it's a common misconception that the space pen was developed by NASA. There's an old joke that NASA spent millions or billions to develop a pen which would work without gravity, while the Russians used a pencil. In reality, pencils were used by both space agencies, but they create lots of graphite dust which damages sensitive electronics and clogs air filters in the life support system. The Fisher space pen was developed on their own dime, and they were sold to NASA for $6 apiece. After the deaths in the Apollo 1 fire, NASA was eager to remove all flammable materials such as pencils from high oxygen environment inside space capsules.