Cold, frigid weather can make horses turn away from ice cold water. They will drink less and it is a common cause of colic, this time of year. Try a clean bucket of slightly warmish water. If he goes for it ...only let him take 5 or 6 gulps and then take the water away for a few minutes and then have a few more gulps, remove, wait, repeat until he doesn't want anymore. do thus twice a day, until you get warmer weather. DO NOT LET HIM GULP DOWN THE WHOLE BUCKET of water in one big drink. He will colic for sure. Do you have trough heater, and insulated water buckets in the stall? Also, never use soap on water buckets. No matter how much you rinse, soap will leave a residue that puts horses off.