In a small saucepan over medium heat, whisk together the water, sugar, salt and vegetable oil. Bring the mixture to a boil then remove it from the heat. Stir in the flour, mixing until it forms a smooth ball.
Heat 3 to 4 inches of vegetable oil in a large, heavy-bottomed stockpot set over medium-high heat until it reaches 375ºF. (There should be a minimum of 3 inches above the oil to prevent it from bubbling over.) Line a plate with paper towels.
Transfer the dough to a cloth pastry bag or heavy-duty plastic bag fitted with a large star tip (optional).
Pipe the dough over the pot of oil to a length of about 4 inches, then using scissors or a sharp knife, cut it so it releases into the oil. (Stand back to avoid any splatters.) Pipe two to three churros into the oil at a time, frying them until they're golden brown and cooked through.
Transfer the churros to the paper towel-lined plate to drain for 2 minutes, then while they are still hot, roll them in the cinnamon-sugar mixture. Repeat the frying and coating process with the remaining dough.