Place the mangoes with water to cover, in a sauce- pan and bring to boil.
Simmer for another 10 minutes at law flame.
You can use pressure cooker to cook mangoes
Drain off the water and then peel the mangoes. Take out the pulp with spoon and place pulp in a deep bowl. 
Add 2-3 cups of water. Let it cool and then strain.
Add sugar, salt, cumin seeds, red chilli powder, chat masala as per taste and mix well.
Refrigerate till it is cool and serve chill or add crushed ice cubes and serve in tall glasses with few mint leaves floating on top.