Preheat your oven to 350°F (176°C) and line a cupcake pan with liners.

In a large mixing bowl, combine the flour, sugar, baking powder, and salt. Set aside.

In a medium-sized bowl, mix together the milk, vegetable oil, vanilla extract, and eggs until well combined.

Pour the wet mixture into the dry ingredients and beat until everything is well incorporated.

Gradually add the water to the batter, mixing on low speed until the mixture is smooth and uniform. Be sure to scrape the sides of the bowl as needed to ensure all ingredients are fully combined. Note that the batter will be very thin.

Fill each cupcake liner halfway with the batter. Bake for 15-17 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Remove the cupcakes from the oven and let them cool in the pan for 2 minutes. Then, transfer them to a cooling rack to cool completely.

To prepare the frosting, beat the butter in a large mixing bowl until creamy and smooth.

Gradually add 2 cups of powdered sugar, mixing until fully combined and smooth.

Add the vanilla extract and 1 tablespoon of water or milk, mixing until smooth.

Incorporate the remaining powdered sugar, mixing until the frosting is smooth.

Adjust the consistency with the remaining water or milk as needed, and add a pinch of salt to balance the sweetness. Mix until the frosting is smooth and fluffy.

Using a piping bag fitted with an Ateco tip 844, pipe the frosting onto the cooled cupcakes. Enjoy your delightful vanilla cupcakes!