Preheat oven to 375. In large mixing bowl beat butter and peanut butter with electric mixer on medium to high speed for 30 seconds. Add sugar, baking soda, and salt. Beat until combined, scraping sides of bowl. Beat in water, egg, and vanilla until combined. Beat in flour until combined. Beat in as much of the rolled oats as you can with mixer. Stir in any remaining oats. Stir in raisins and oat cereal.
Drop dough by scant 1/4 cupfuls about 3-inches apart onto an ungreased cookie sheet. Flatten slightly. Bake for 10-12 minutes or until edges are lightly browned. Cool on cookie sheet for 5 minutes. Transfer to a wire rack and let cool completely. Store cookies in a tightly covered container for up to 5 days or freeze for up to 3 months.