In this classic Indian recipe the lentils and rice are not cooked, but soaked overnight in water, which softens and ferments them. Then they are pureed. The chlorine in tap water can inhibit the softening of the lentils, so it is best to use bottled spring water. Urad dal are skinned, split lentils that are available in Indian groceries. Typical lentils found in the supermarket will not substitute in this recipe.
Asian Cooking Magazine