Do you ride it? If not, and you can't help yourself, just drain it in the fall and refill in the spring. Leave it empty.
So I've had several bikes over the years (haven't we all) and I have had varying experiences. Some bikes had nothing but water wetter in them for years and I never had any corrosive problems. Other bikes, I'd see some sediment in the cooling system after a season of water wetter. Nothing major, but noticeable specs of crud. Aging radiators, water pumps, who the hell knows the exact reason why it forms on some bikes and not others.
I've always made it a habit to put anti freeze in over the winter, one, I know there's a zero percent chance of water pooling in any part of the motor and freezing. Secondly, on those rare semi warm days, I can fire up the bike and run it up and down the street, just cause without burning up the water pump or over heating the motor. And third, since doing so, I haven't had any issues with sediment build up in any bike I've had. I am a firm believer that anti freeze provides some anti corrosive properties and for my use, this serves as the best of both worlds solution. Obviously I am sure to flush the cooling system for the spring time once or twice before calling it good.