Cross-contamination occurs when gluten-free foods come into contact with foods that contain gluten. It can happen during the manufacturing process, for example, if the same equipment is used to make a variety of products. Some food labels include a may contain statement if cross-contamination is likely.
After getting a tattoo, swimming must be avoided until the skin has stopped peeling and all scabs have fallen off. For most people, this means waiting a minimum of two weeks.
There's nothing stopping you from having a shower / bath the same day as getting it done, as long as you don't soak the tattoo, as that will bring the ink out. So a quick shower won't do any damage at all. After about 2 - 3 weeks it should be fully healed and you can be free to soak.