its been green and watery
It sounds like your bird has an infection of some sort. Without a doubt, I think there is a problem with your bird, it is sick. It sounds like canker, but who knows.
If you can open the birds mouth, can you tell me if you see any yellow/orangish cheese looking growths anywhere, especially in the back of the mouth? If so, canker is the culprit and you'll need antibiotics ASAP, and continue treating water with organic apple cider vinegar. If the bird is also drinking a lot, you can be pretty sure it is canker. Most vets can give you medication, even if they're not an avian vet metronidazole will work, all vets carry that.
I think you have a few options, one of course is to take it to an avian vet if you don't mind spending $50-200 on this bird's well being. The other is to treat the bird for a multitude of different things it is likely to be if you cannot be sure what it is. Assuming the bad things that can happen to a dove are similar to a pigeon (which I imagine they are), your culprits are canker, worms, or some other bacteria or parasite. I would treat for canker and worms. Broad spectrum 4-in-one type medications are available for treating birds just like this, when you don't know
exactly what it is, but you think it could be one of 4 different things. There are many medications like this. To help a bit with this, although it may not cure it, you can treat the bird's water with organic apple cider vinegar, dose 2 teaspoons per liter of water.
I would get it to a vet or get treated with one of those medications immediately.
I would also quarantine this bird from your other birds.