Stir masa harina and water together until dough holds together in a ball. Turn onto a working surface that has been dusted with masa harina. Knead quickly into a smooth ball. Divide dough into twelve pieces. Roll one piece into a ball. Place between two sheets of wax paper and flatten slightly. Press tortillas (still in wax paper) in a tortilla press until tortilla measures about 6 inches in diameter. Repeat with remaining pieces of dough, stacking tortillas, still sandwiched in wax paper, under a damp tea towel until ready for use. When you're ready to cook the tortillas, preheat a seasoned cast iron griddle over medium-high heat. Remove wax paper from tortilla and heat on griddle, turning frequently until it looks dry and has a golden color, about 1 to 2 minutes. Repeat with remaining tortillas.