I was explaining a recipe to my girlfriend over SMS. I wanted to tell her that for each cup of rice she added to the recipe, she should pour in an additional cup of water, too.
You should add twice as many cups of water as of rice.
That is, if she added, say, 4 cups of rice, she should pour 8 cups of water into the pot.
I know the sentence is comprehensible because she managed to fix the dish, but I am unsure if the sentence is correct or idiomatic.
Can someone tell me if this sentence is OK?