[Tsuwabuki]

For a smaller tattoo, the best thing you can do it just cover it up with a water resistant/proof bandage. I know of teachers who do this during summer months when its too hot to wear a full length sleeve. I imagine you can do the same even in a water situation, as no one is going to be crass enough to demand you open a "wound." Just make sure it's resistant or proof, you don't want it coming off in the water!