How to Breed a Rain Dragon in DragonVale
To breed a rain dragon in Dragonvale, start by opening your breeding cave, or access the Epic Breeding Island. Select your air dragon and water dragon, which are needed to breed a rain dragon. If you don't have an air dragon, you'll first need to breed one by combining a fire dragon with a water dragon. Wait for the breeding time to finish, and then check to see if the resulting egg is a rain dragon, which should be violet with 3 blue waves. If you get the wrong egg, try breeding them again until you get a rain dragon.
Open your breeding cave. You can also open the Epic Breeding Island. Choose the dragons to mate. To make an Air dragon you'll need a Fire dragon and a Water dragon. Wait for the breeding time to finish. The amount of time it takes varies depending on the type of dragon. Alternatively, you can use gems to speed up the process, though it is not recommended since you'll just waste gems. Check to see if you've successfully bred an Air dragon. The egg will be white with a tint of purple- and cyan-colored swirls. Place the egg in a nursery and wait for it to hatch. It takes about 2 hours for an Air dragon egg to hatch. Feed the Air dragon until it reaches level 4 or higher. This is so your Air dragon can be used for breeding. Dragons can only start breeding when they reach level 4. Open the market and purchase a Water dragon. Water dragons are 500,000 gold each. The only other way to obtain this dragon is by breeding two Water dragons together, which seems to be counterproductive. Feed the baby Water dragon. Do this until it reaches level 4 and above. Open your breeding cave. Again, you can alternately access the Epic Breeding Island. Select your Air dragon and Water dragon. These two types of dragons are needed to breed a Rain dragon. The Epic Breeding Island may increase the chances of you getting a Rain dragon. Wait for the breeding time to finish. Time varies based on type of dragon. Check if the resulting egg is a Rain dragon egg. A Rain dragon's egg is violet with three blue waves. If you got the wrong egg, re-breed the dragons until you get the Rain dragon egg. Place the egg in a nursery and wait for it to hatch. It takes 8 hours for a Rain dragon's egg to hatch. Hatch the egg once it's ready. Congratulations, you now have a Rain dragon! 
Open your breeding cave. Choose the dragons to mate. Wait for the breeding time to finish. Check to see if you've successfully bred an Air dragon. Place the egg in a nursery and wait for it to hatch. Feed the Air dragon until it reaches level 4 or higher. Open the market and purchase a Water dragon. Feed the baby Water dragon. Open your breeding cave. Select your Air dragon and Water dragon. Wait for the breeding time to finish. Check if the resulting egg is a Rain dragon egg. Place the egg in a nursery and wait for it to hatch. Hatch the egg once it's ready. 