In a saucepan, combine the lemon zest, lemon juice, granulated sugar, and water. Stir well to dissolve the sugar.
Bring the mixture to a boil over medium-high heat, then reduce the heat to low and simmer for about 25-30 minutes, stirring occasionally, until the jam has thickened. It should coat the back of a spoon.
Pour the hot jam into sterilized jars and seal them tightly. Let cool completely before storing in the refrigerator.
Notes
This jam can be stored in the refrigerator for up to 3 weeks.