Preheat oven to 325 degrees. Line cookie sheets with parchment paper; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, shortening, and sugars until light and fluffy. Add the egg, water, and vanilla; beat until combined.
Add the salt, baking soda, and flour to the bowl. Mix until just combined, then stir in the oats and raisins until just mixed. Spoon dough onto baking sheets by rounded teaspoonfuls, spacing about 2 inches apart. These cookies spread quite a bit, so give them some room to grow. Bake for about 15 minutes or until golden and just set in the center. Allow to cool for 5 minutes on the baking sheet, then move to a rack to finish cooling.
Store cookies in an airtight container for up to a week.