You can also use this technique to create drops of water falling in front of a background by copying down the layer with the drop. just make sure that the water drops show the reflection upside down.
But if you want to make sure all your drops are clear, keep the original drop hidden at the top of the layers, and just use it to copy down each time you want a new drop. Once you reduce a layer, you shouldn't copy that layer to enlarge it because it will become a bit blurry. It's okay to reduce a layer, but don't enlarge that same layer or a copy of it, once you reduce it. That's why you should always keep an original layer, so you can always start fresh!
Thanks for taking the time to read my blathering explanation of my process! I hope it helps you in making some great sketches!