Encourage him to drink

Make water available. Allow the horse to drink as much as he wants. If possible, offer him lukewarm water---it’s a myth that drinking cold water will cause an overheated horse to colic, but he’s likely to drink more if the liquid is tepid. However, do not try to force water intake with syringes, hoses or other artificial means. If water enters a horse’s lungs, he can develop pneumonia.

Use electrolytes sparingly. If you have powdered electrolytes, add a scoop to a bucket of water, but offer plain water also. Avoid giving a horse with heat exhaustion electrolyte paste because it may throw off his metabolic balance or contribute to dehydration.

Do not give your horse any medication. A dehydrated horse’s kidneys are already taxed, and drugs can push them over the edge to failure.