Hanging up on the fence, especially if it is near his water bucket, will make it an enticing toy and keep it clean. Some horses won’t lick on a rock on the ground if it is dusty and dirty. No matter what salt you choose, make sure your horse has access to salt daily—and of course, make sure water is clean and fresh.
http://www.redmondequine.com/how-do-you-hydrate-your-horses/
Necessity of Water. No matter what you do with your horses, water must be a first priority. When I led out big pack trips through the Rocky Mountains, we had to make sure to take trails that bordered streams and that the horses were allowed to drink each time we crossed a stream.
http://www.redmondequine.com/how-do-you-hydrate-your-horses/
You can add water and administer via dosing syringe, add the electrolytes to your horse's feed or add the electrolytes to their water. Each way works equally as well, just figure out what your horse prefers to ensure they are consuming the added electrolytes.
http://www.southernstates.com/articles/equine-hydration.aspx
A dehydrated horse will take frequent, shallow breaths as his body tries to shuttle resources from one system to another. A typical breathing rate is between 8 and 12 breaths per minute. Check how long it takes the capillaries to refill by pressing gently on the gum near your horse’s upper teeth.
http://www.redmondequine.com/dehydratedhorse/
Use the pinch test as a quick and easy way to tell if your horse is hydrated. Pinch a bit of skin at the point of your horse's neck and release it. Count the seconds until the skin lies flat. If it flattens back in place in less than a second, no worries your horse is hydrated. If it takes more than three seconds to flatten your horse is dehydrated, use the tips above to get more water in him.
http://www.southernstates.com/articles/equine-hydration.aspx
Too often in the past, I’ve seen horses that don’t drink much water have bouts with colic and mild digestive upset. No matter what you do with your horses, it’s important to make sure they have regular and constant access to fresh clean water—especially those that are finicky, like my horse Dually.
http://www.redmondequine.com/how-do-you-hydrate-your-horses/
Salt is a necessity in a horse’s diet. You know that if you eat a bag of salty potato chips, you’ll crave a drink. I wouldn’t eat chips unless I had my water bottle in my hand. The same is true with horses—giving salt can encourage horses to drink more.
http://www.redmondequine.com/how-do-you-hydrate-your-horses/
Soak it and mash it in feed. Get extra water into your horse through their food. Soak your hay flakes or cubes prior to feeding. One flake of wet hay can absorb 1-2 gallons of water. This can have a huge impact on your horse's water consumption.
http://www.southernstates.com/articles/equine-hydration.aspx
When your horse is resting, try to count his pulse for 60 seconds—if he’s restless, try 30 seconds and double the amount. (Try to avoid the common advice to check for 10 seconds and multiply by 6; the results will be less accurate.) A resting heart rate higher than 60 might indicate dehydration.
http://www.redmondequine.com/dehydratedhorse/
Keep Your Horse Hydrated. Make sure your horse has easy access to water at all times. He shouldn't have to go searching to find a clean water source. Provide your horse with squeaky clean water. Tipped over, leaky, funky smelling water buckets aren't appealing to drink from.
http://www.southernstates.com/articles/equine-hydration.aspx
how to hydrate horse
To hydrate horse: Provide horse with squeaky clean water, tipped over, leaky, and funky smelling water buckets aren't appealing to drink from.  To  hydrate horse Make sure your horse has easy access to water at all times and he shouldn't have to go searching to find a clean water source and tipped over, leaky, funky smelling water buckets aren't appealing to drink from.