In the bowl of the stand mixer, with the paddle attachment, add the sugar and the meringue powder.
Mix to combine and break up any lumps.
Add the water and mix on low until the icing starts to come together.
Turn the mixer up to medium and beat for 4-5 mins, or until light and fluffy and holds a stiff peak. (You may need to add more water to reach the desired consistency for the piping.)
Keep your icing covered, either with cling-film or a damp cloth, when not in use, or it will start to dry and set.
The stiff consistency is perfect for making things like royal icing flowers or piping 3 dimensional designs.
For the consistency for writing or piping borders, the consistency should be similar to mayonnaise. (You gradually add water to the icing until this is reached.)
For flood consistency, (this is the main inside icing you will be filling the cookie with), add water gradually, until you have a runny honey consistency.