No! You don't have to use Apple Cider and water warm. The choice is yours. Whenever I am having the mixture first thing in the morning I use warm water. But during the course of the day I have it with room temperature water. I add a teaspoon of honey which makes it more tolerable to ingest.
I do believe the choice is yours and what makes you comfortable. Which either way taken it is still effective.
It works wonders for sinus problems, digestion, yeast infection. And I can go on.
Hope it works for you. All the best.