I had a fussy horse and would put electrolytes in his water at home. It does change the taste of the water so it may take some time for your horse to get used to it. But them when we’d travel to competitions, I’d continue with the electrolytes and the water would taste familiar to him so he’d drink it.
If you are concerned about colic, I would feed beet pulp soaked in water to increase your horse’s hydration and keep things moving through his gut. http://www.vdbequestrian.com