I just finished making royal icing. I wanted to make roses and swirl flowers with it. I followed the instructions on the Wilton book. It asked for 5-6 Tbsp of water. I added 6 and I think I made it too thin. I don't know what to do!!!! I started piping my roses, and they looked okay but after a minute they started losing their shape and melting. Is there any trick to salvage this by letting the icing dry or something? I know I should have probably added more sugar, but the icing has been separated, colored, and in bags ready to use. I really wouldn't want to start again. I think I learned my lesson well and I will try again soon, but could I do something with this one so that it can harden as it sits in the bags? 
If you let it sit in the bag, it will harden for sure. But you won't be able to pipe it out.
I would empty the bag and add more PS. I know it will be a pain, but you don't have to toss the whole batch, just empty one bag, add more sugar, and re-fill the bag. Try one color at a time, so you get a feel for how much you have to add on the first bag, and there won't be so many trial and errors on the subsequent ones.
Good luck to you.
I agree with karateka.....just empty the bag and add more PS to the batch. In general, when the recipe calls for a certain amount of water (esp. with RI) take it with a grain of salt because it all depends on the level of humidity in your environment. Don't get upset....get PS! 
Good luck!
Thank you all for your responses. Karateka: I did what you told me. It was a pain, but it had to be done. I struggled with it but I managed to thicken it. I learned my lesson. I will also try the cornstarch if it happens again, but I will also listen to your other advise and will not add all the water at once.
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