If using fresh tamarind, then add it to a bowl of warm water and let it soak for 15 minutes. Then crush the soaked tamarind with fingers to extract the juice. Filter this juice into another vessel and repeat the same with the remains, 2-3 more times by adding them to fresh water and squeezing out the juice. This is tamarind water. Use it in recipes like Rasam or Puli Aval.