In a large pan over medium heat, add the tamarind and water. Stir well.
Bring to a boil and cook until the tamarind softens.
Mash the tamarind with a potato masher until it becomes mushy. Cook for an additional two minutes.
Remove the tamarind mixture from the heat and place in a strainer over a bowl. Reserve the tamarind liquid. Set the leftover tamarind pulp aside for another use.
In a pan over medium heat, add the oil and the cumin seeds. Heat until the seeds begin to sizzle.
Pour in the reserved tamarind liquid, jaggery powder and ginger powder. Stir to mix well.
Boil the mixture for 3 to 5 minutes. If using chili flakes, add them now along with the salt.
Simmer the sauce until it begins to turn thick and sticky. Remove from the heat and serve as a dip with samosas and other Indian street foods. Tamarind sauce can also be used as a condiment to flavor stews, braises, and curries.