Halve the strawberries, place in a large jam pan with the water and soften for 10-15 minutes over a moderate heat.
Add the lemon juice and jam sugar, stirring to dissolve the sugar while bringing to the boil. Continue to boil steadily at about 104 C, stirring from time to time, for 20-25 minutes.
Use the wrinkle test to check the setting point then, when ready, take off the heat and skim off any scum from the surface.
While still hot stir in the Pimms and leave for a few minutes to allow the alcohol to burn off. Ladle into warm sterilised jars and seal.
It will keep for up to 6 months unopened. Once opened refrigerate and eat within four weeks.