Yep, you can dilute them and they keep well even when opened
I keep mine in the freezer! When I want one for lunch at work I wrap it in foil and put it in the fridge at work and by the time its lunch time I have a lovely ice cream!!
So they don't have to be eaten (drank) within 15 minutes?
I wish I could do all this - but I don't like Tetras! (They taste like chemicals to me!)
Strange how tastebuds vary isn't it.