How can a Catholic church provide gluten-free hosts (for those who have an allergy to wheat/gluten) when the recipe for the bread is water and wheat?
It can’t. What it can do is offer low-gluten hosts for those celiacs who can tolerate a very small amount of gluten on an occasional basis. Those who cannot tolerate any gluten at all cannot receive the host. They can receive the precious blood, consecrated for them in a separate cup if need be.