What is the best way to get a watermark out of a shirt?

To remove a watermark from a shirt, first, identify the fabric type and check the care label. Gently dab the stained area with a cloth soaked in a mixture of water and mild detergent, avoiding harsh chemicals that could damage the fabric. Rinse with cold water and launder as usual. If the stain persists, consider using a stain remover specifically designed for the fabric type or seeking professional cleaning assistance.