You can put almost any drink into a Hydro Flask. But there are some things you shouldn’t store in a Hydro Flask, especially for an extended period of time.
Lemon Water: The lemon juice can rust the inside of the bottle after a prolonged period of time.
Milk: When milk is stored in the flask for a long time, microorganisms can grow. Milk should be kept refrigerated so that it doesn’t spoil.
Bleach: Don’t store bleach or chlorine in the Hydro Flask — this will damage the interior.