Wash rice and urad dal. Soak them both in water for 4-5 hours. Soak fenugreek seeds (a ½ spoon) with urad dal. This helps to maintain the fragrance and coolness of the batter. Now grind the soaked urad dal, adding some water into the mixie / grinder. Grind it well till it turns into a frothy, smooth batter.
Add sufficient water to the soaked rice and grind it well / until you reach the desired consistency. Now mix the Rice batter and Urad dal batter in a vessel and add salt according to taste. Mix everything well with your hands. Let it ferment for 8-10 hours.