Put them in a bowl with the water and sugar and cover tightly with cling film then place bowl over a pot of boiling water for 1-2 hours or until the juice is extracted.
Strain through a fine sieve and allow to chill in the fridge until serving.
For the Panna Cotta, boil the milk, cream, sugar and vanilla pod in a small sauce pan. Once up to the boil add the gelatine and stir until it has completely dissolved.
Divide the panna cotta mix into four small pudding moulds or ramekins and allow to set in the fridge for 3-4 hours.