Take 1 cup of fresh curd (dahi) and add it to a mixing bowl.
Add 3 cups of cold water to the curd.
Mix the curd and water using a hand blender or a whisk until it becomes smooth and frothy.
Add 1/2 teaspoon of roasted cumin powder (jeera powder), 1/2 teaspoon of black salt (kala namak), and a pinch of regular salt to taste. You can also add chopped coriander leaves and green chilies for added flavor.
Stir the mixture well to combine all the ingredients.
Pour the chaach into glasses and serve chilled.