When combined with dressing, cabbage (like other vegetables) will “sweat”, getting rid of the water that’s inside. So, it’s normal for coleslaw to get a little bit watery after a while. Make your coleslaw right before serving to make sure it won’t become too watery. Or, if you want to make it the day before, you can toss cabbage with some salt and let it sit at room temperature for up to 2 hours. Then, drain the water by squeezing with the hands, then mix with the dressing and the rest of the ingredients. Refrigerate before serving.