Place water and milk in 2-qt saucepan and bring to simmer. Meanwhile, melt butter in skillet until foamy. Add oats and toast 1-2 mins.
Add oats to liquid, simmer med-low until mixture starts to thicken, appx. 20 mins. Add salt, stir, and continue simmer an additional 7-10 mins. Off heat, cool until thickened. Add desired flavorings and serve.