Crochet hook maintenance should be done on dry hair only. Dry hair is less susceptible to breakage because keratin protein — the stuff hair and nails are made of — is more durable when dry.
Keratin chains are held together with hydrogen bonds. Water (which is hydrogen + oxygen, H2O) breaks those hydrogen bonds apart when hair gets wet. The disjointed, unlinked protein chains in dampened hair make it really easy to snap each strand until your hair is dry again. There’s strength in numbers: So the more linked keratin proteins your hair has, the more durable your hair strands will be.
Here is an analogous example: Fingernails are easy to bend and tear when wet; similarly, each hair strand is more fragile when damp as well.
Because of this, try to crochet hair only when it’s 100% dry.