Is your Pullip wigged or rooted? If it's a wig, it's just held on by glue around the edge, and is easy to reattach if it comes off. As far as I know the glue wont be affected by water, but the wig might be easier to wash if it's removed first. If it's a rooted scalp, just take care not to get water inside the head, or remove the scalp for washing seperately