Place water and sugar in a container with a tight fitting lid. Shake vigorously for 3 minutes. Let rest for about 1 minute. Shake again for 30 seconds before using.
Alternatively, you can heat the water and sugar in a small saucepan, stirring until the sugar has dissolved. Cool completely before using.
Margarita
For each of your margarita layers, add the ingredients to a high-powered blender. Process until smooth, adding additional ice if needed, to get the consistency to that of a thin sorbet.
Rinse the blender between batches and keep the previously prepared layers in the freezer until ready to assemble.
Use a spoon to place your first layer in the glass. Repeat with the next remaining layers, spooning the mixture first around the edges and then filling in the middle. This helps keep the layers from running together.