Scrub carrots and wash under running water. Peel and cut carrots into batons. Take eighteen cups of water in a large jar or a clay pot (matka), which will be able to hold four litres of water.
Add carrots, mustard powder, salt and red chilli powder and mix. Cover the pot with a muslin cloth and tie it up around the rim.
Let it stand in sun for three to four days. When it gets ready keep it in the fridge to chill. Pour into tall glasses with some pieces of carrot. Serve chilled.