1. Puree the raspberries in a blender or food processor. Rub through a nylon sieve to remove the pips.
2. Mix the puree with the water and honey and pour into a rigid freezerproof container. Cover, seal and freeze for about 3 hours, until half-frozen. Turn into a bowl.
3. Whisk the egg white until stiff, then whisk into the half-frozen raspberry puree. Return to the container, cover, seal and freeze for about 2 hours, until firm.