In a medium bowl, mix together milk, water, melted butter, and vanilla extract. In a small bowl, thoroughly mix flour, sugar, and salt. Whisk flour mixture into milk mixture until batter is smooth. Cover and refrigerate 2 hours.
Warm a medium skillet over medium-high heat. Coat pan with a small amount of vegetable oil and pour in about 2 tablespoons of crepe batter. Swirl pan to allow batter to spread out thinly. Cook until edges are crispy and golden, then flip to cook other side until lightly browned. Repeat with remaining batter.