David Oyelowo’s directorial feature debut, “The Water Man,” plays like a kid-friendly throwback to Steven Spielberg’s ’80s movies. It’s a coming-of-age story filled with adventure, friendship, and some serious topics that don’t overshadow its young protagonist’s hopes. The story gives its hero, Gunner (Lonnie Chavis), the chance to grow from a shy graphic novel nerd with a love of detective stories to a fearless wanderer looking for a cure to help his mom. His bravery lands him in trouble –– because what’s an ‘80s adventure movie without at least a little bit of danger –– but the movie doesn’t demean the character or his efforts. It’s along for the fun of the mystery, too.