No coating needed. All you need is to re-flow the ABS. Feels like pottery after this simple operation: https://youtu.be/iLaGJwCCz-E?si=a1gccp8EI9sGzt-e

Do you really want almost-boiling-water in ABS? I wouldn't do that.

Reflow happens at 200°C, out gassing any 3D-related harmful stuff.

Equal to inject-molded ABS cutlery.

Maybe I'm too careful but I wouldn't use plastic cutlery on hot food either. Also, the glass transition temperature of ABS is only 105 °C, so It's probably not too strong when filled with 100 °C water.

I have already made all kinds of tests. Only restriction was that you cannot make open flame cooking pot, because it starts combusting too easily.

How did you test the water quality after storing it in an ABS container? How would you notice if something from the ABS dissolved in the water?