Cut the nectarines lengthwise in half, twist the halves apart to remove the pits, and peel, using the tomato peeling technique described.
Put the nectarines, sugar, and lemon juice in a food processor or blender and run until puréed. Add the water and run the processor until well mixed.
In a large bowl, whip the heavy cream by hand until it thickens to the consistency of yogurt. Add the nectarine mixture to the bowl and stir well. Transfer to an ice cream maker and freeze according to the manufacturer’s directions. Serve right away if you like a soft consistency. For a firmer ice cream, transfer to a container, cover, and freeze for 2 hours.
The ice cream can be frozen for several days before the surface begins to crystallize.