It seems you're looking for a 13-letter word or phrase that fits the clue "Dat het hele gezin in bad is geweest, komt door je partner." This appears to be a Dutch word puzzle or cryptic clue.
Given the context, a possible 13-letter phrase could be **"familieuitje"** ("family outing") since a family outing can involve the whole family, possibly to a location where they might go swimming or take a bath together. However, this is only 12 letters.
If the clue refers to something specific and common in Dutch culture, it could be a bit challenging without additional context. Do you have any other hints or ideas?