My experience fits with what TimoV says. It is not the strong solution of methanol based fluid from the bottle that freezes and stops the washer working.
Why bother?
Because screen totally obscured by dried salt spray on winter evening. Washers would have cleared it but were frozen. Same happened in daylight a few days later.
2003MY Disco2 ES
LR dealer says it does not have the wiring to allow heated jets to be fitted.
After market? Difficult?
I am not really concerned about headlamp washers or rear washer.