I used them a few years ago and never could gret it to be anything but a decerative mug. They just chip off even if you're careful. sorry...

Waterslip decals are fun to use - but would never stand up to washing or daily use. I have an inkjet printer, so I buy inkjet decal paper. You seal it (after printing) with clear spray paint. Best used for items that are decorative only.

The decals you can make on your inkjet are not intended for daily use or even meant to be washed.
The type of decals that you see on store bought mugs are the type that are fired onto the ware.
Now there's another type of "decal" that out there and it's used mainly for advertising applications. It's called "Sublimation". But the setup can cost thousands of dollars. And the artwork can be heat set onto a mug using a special mug "wrap" that heats the dacal. But it's not food safe or suunlight proof as it fades over time. You use your Epson printer and special inks and paper. Regular inkjet inks are not waterproof or heatproof enough.

Here is a link that might be useful: Sublimation