If you do not have buttermilk handy, you can add 1 tsp of white vinegar to 1 and ¾ cup warm milk and let it stand for 5 minutes. Then use this mixture in the waffles instead of buttermilk. I do this very often when I do not have buttermilk with me and it turns out very good.
If the batter turns out too thick, add 1-2 tbsp water