The liquid is a very important ingredient in your smoothie. It’s what helps the blender break down the fruit to make them creamy and delicious. Technically, just about any liquid will work, you just have to think about what your goals are for this smoothie. Water will not add any additional calories, but might not create a satisfying smoothie. Yogurt and higher fat dairy milks will add fat, flavor and make for a deliciously decadent smoothie, but will increase your calorie count. I find unsweetened nut milks or pure coconut water is a happy medium.