Spawning small pools of water

Hi there, 
I'm trying to spawn some small pools of water into these oasis' I've created and having some trouble. These are all in a custom dimension with custom biomes. 
I've learned the basics of placing features, including custom trees (though the ones in the screenshot are modified acacia trees). 
I've copied the vanilla spring into a new file and added the "valid blocks" from the environment but haven't had any luck spawning them in. I even spammed them across all biomes in my new dimension, just to see if it was an issue with elevation with no luck.
I think that a more basic approach might be needed. I'm basically wanting a small blob of water with mud bordering the sides and bottom in case it bumps into other biomes. 
Any help would be appreciated! I'm willing to try anything!