Measure the water into a small bowl, sprinkle the gelatine powder over the top of the water and set aside. The gelatine will absorb the water, this will take 5-10 minutes.
In a saucepan combine the cream, white chocolate and strip of lemon zest. Heat the cream over a low heat whilst stirring until the white chocolate has melted.
Remove the lemon zest, then add the activated gelatine to the warm cream and chocolate. Stir over a low heat for 1 minute.
Remove the saucepan from the heat and beat the mousse for 3 minutes at low speed, or use your elbow grease and whisk the mouse by hand. This helps cool the mousse.
Divide the blueberries and place in the bottom of six glasses.
Pour the white chocolate mousse over the blueberries, dividing the mix evenly amongst the four glass.
Chill in the refrigerator for 60 minutes before serving. This mousse can also be prepared 24-48 hours in advance if you wish.