Statistics for actual storage

I like the statiscs and all but what i want its how much of an item i have in storage and i dont mean the total, like i have 10k coal and 7k water thats great but it thats all into lets say steam power then i dont actual have that coal/water available. I would like the option to mark certain containers to show up in a new window as a 'Storage' like the statistics window so i know how much i actually have available that will be sent to production lines when needed.

Or have an option to mark a container that doesnt count toward the 'Statistics'