Preparing For Freeze

Louisiana is looking at a hard freeze next week. I do have access to stalls, but my horses refuse to drink water when they are stalled. I have cleaned the troughs like 15 times, tried everything but they just won’t touch the water.

Is it better to leave them in the pasture where they will drink or stall them and risk them not drinking?

I have three senior horses (all 20+ yrs old). They’re pretty hardy, except for one who had colic a year ago from dehydration. They do have access to shelter in the pasture, though I can’t imagine a tin lean-to would keep them warm.