No water needed! I try to collect a little more than just the leaflet, so maybe a full leaf, and I put it in a gallon size ziplock bag. Most leaves will last a week or more with a little care. Check the bag daily to make sure the condensation is minimal. Wipe down excess from the side of the bag so it doesn't cause the leaf to mold. The reverse of that would be the leaf getting dried out. If that is the case, put 1 or 2 drops of water on a 1" square of paper towel and put it in the bag to increase the moisture. If you are checking it daily, you should be able to adjust enough until it pupates. Once it pupates, you can choose to cut open the mine and separate it from the leaf. It still needs some moisture for the adult to eclose properly, but very minimal. You probably won't have to do anything at all. Sometimes I will take the pupa out, photograph it, put it in a plastic condiment cup with lid (think jello shots) and continue to check it daily. It's better to have a little less moisture than too much, in my experience. In fact, I still lose many to mold, but there are so many factors. Charley Eiseman has a post on his website about how he rears leafminers. If you haven't read that, you should. Good luck! Tag me when you post your photos!!