Does this line mean right?

I wanted to say to my friend that, I did excercise for 10 mins and after its completion, I waited for 30 mins and then I drank water. I constructed it as

"After 30 mins of doing the excercise, I drank a bottle of water"

But I immediately felt that this line is ambiguous. I think this line could also mean that I did excercise for 30 mins and then drank water. Was I correct ? If not how should I say it ?