To achieve waterproof quality with UV ink jet ink, it is important to use UV adhesion promoters. The short answer is that yes, UV ink is waterproof, but it also depends. Unlike solvent-pad printing inks, UV ink is formulated to adhere to a wide range of materials. Each ink has its own characteristics. For example, the Natron 160 series UV ink has excellent adhesion to glass when placed in a dishwasher. It can pass over 600 industrial washes.
We recommend always using a UV adhesion promoter with UV ink as well as performing adhesion testing on your specific product prior to mass production.