I, like others, added a bit of water to thin the yogurt dressing. (epicurious.com)
And since I don't generally have buttermilk, I usually thin some yogurt as a substitute. (rookiemoms.com)
Add the 1 cup of thin yogurt, buttermilk or cultured milk and stir well — until you can see the bubbles on the top, which means that the soda and the liquid have begun to act with each other. (healthyflour.com)