Can Water From Thermo Flask Be Used For Preparing Nan Pro?

Hi , My baby girl is in 5th month. I feed her NAN PRO1. I boil water and keep in a thermo flask. So while its time for feeding, I mix hot water with the milk powder and then cool enough so that baby can take.

Is this correct ? Also my doubt is the quantity of water + milk I should give to my daughter now ? Please guide