DO NOT, I REPEAT, DO NOT LET IT OUT INTO THE WILD! It is a Pet, and will not survive outdoors. If it does survive, it will end up a "pest" rather than a pet to someone, and could end up in a trap. Any way you look at it, it would not be good for the little Rat dude.
Domesticated rats are as vulnerable as babies. Pet rats should never, ever be released into the wild. They would have no idea how to find food in the wild or what would be safe to eat. The same goes for water. Wild rats learn what to eat from what their parents eat. They know from the second they're born just by the taste of their mother's milk. A domesticated rat dumped out into the wild would have no experience of the foods out there, or how to find them.