Horse wont swallow water and generally not interested in food...urgent?

It sounds as though he either has something stuck in his mouth, his throat, or his esophagus. He needs medical attention asap. Something like this can lead to complications that are life threatening at any moment. If there is something stuck, and having gone on this long, the tissue is likely to be swelling and worsening the condition, and also making removal that much more difficult to achieve. He could aspirate the water he is trying to drink into his airway. The list goes on. I would treat this as an emergency and get the vet there right away.