Your bird probably either has an infection or a disease. Please Find an Avian Vet to examine your bird right away to determine what is causing this.
If your bird drinks from a dish instead of a water bottle then it is very possible it is a bacterial infection. Our avian vet warns that if we allow our birds to have a bowl of water in the cage for more than 3 hours, we risk bacterial infection.
Birds eat and then drink and food particles get in the water. Then they turn around and sometimes poop in the water. Then the bird bathes or dips it's head in the bacteria laden water. You can see how it is possible that a bird could end up sick from all of this.