in a METAL or glass bowl (not plastic) stir the Powdered sugar and the meringue powder together
add 5 Tbsp warm water and mix until it's mostly all wet
Using a mixer beat for 10 mins on low speed (less with a heavy duty mixer, slightly more with a hand mixer)
add 1/2 to 1 tsp of water at a time until the consistency is right.
Video
Notes
I keep my stencil on hand and once I THINK the icing is thin enough I start testing it. For designs with larger openings it will be slightly thicker than small and detailed stencils.