Shell tamarind and place in a medium bowl.
Bring 3 cups of water to a boil and pour into the bowl, making sure the fruits are all well covered with the water.
Cover the bowl and leave to stand until cool.
Place a fine sieve over an empty bowl, set aside.
Wearing a food-grade glove, squeeze the tamarind in the water to separate the pulp from the seeds. Most of the pulp would have dissolved into the water anyway as it was cooling.
Pour into the sieve to strain out the juice.
Pour seeds back into the first bowl and add the remaining 1 cup of water, mix well and strain. Discard the seeds.
Add the lemon juice and jaggery or other sweeteners to taste, stir and store in a clean bottle in the refrigerator.