In a medium saucepan place the rice and 2 cups water and bring to a boil. Reduce heat to low. Cover and simmer 20 minutes or until cooked.
In a large saucepan bring the remaining 10 cups water to the boil. Place chicken in the saucepan. Stir in kaffir lime leaves, lemongrass, spring onions, garlic, tomatoes, fish sauce, mushrooms, coriander, Thai chillies and tamarind soup base. Cook for 30 minutes or until chicken juices run clear.
Remove chicken from saucepan. Debone, chop and return meat to the soup and discard the bones. Serve over cooked rice.