Take 2 large lemons, wash them thoroughly, and cut them in half. Squeeze the juice from the lemons into a bowl, ensuring you extract about 60-70 ml of lemon juice.
In a large pitcher, add 1 litre of cold water, the extracted lemon juice, 4 tablespoons of sugar, and a pinch of salt. Stir well until the sugar dissolves completely.
Add ½ teaspoon of roasted cumin powder and ¼ teaspoon of black salt (kala namak) to the pitcher. Stir well to combine all the ingredients.
Taste the Nimbu Pani and adjust the sugar or salt according to your preference. If you want a more diluted drink, add more water.
Pour the Nimbu Pani into glasses filled with ice cubes. Garnish with a few fresh mint leaves and a lemon slice. Serve chilled.