How tho? Undercover brella?

Honestly, I think they do just fine. But if they want to go swimming I think they have to put some substance on their skin.

Umbrellas

But the brellas just go flying after holding it out for a few seconds

The weaponized brellas

TrinityRBG made a good video on this https://m.youtube.com/watch?v=gkYFjB5vv34

Inklings and Octolings are perfectly fine with rain, their bodies can only handle a specific depth of water. They can take showers, they just can't be in water up to their waists. Thank YouTube for this knowledge

True