Joe, and others;
I guess the water here in Central Kentucky is fairly soft because I've never used distilled water in any radiators,and we have a still in the laboratory that makes three gals/hr.I do use the distilled water in our batteries.
Maybe the reason we don't have scale in our radiators, is the fact that we use the green coolant(Prestone). Shhh, don't let everyone know we are using the best and most popular brand of antifreeze.
Bill Lewallen Lexington,Ky. The Bluegrass State, where the grass is really green, and we use the Green coolant.