In a small heavy saucepan, bring the water and sugar to a boil. Cook and stir until sugar is dissolved. Remove from the heat; cool slightly.

Place the watermelon, strawberries and lemon in a blender; add sugar syrup.

Cover and process for 2-3 minutes or until smooth.

Strain through a mesh and discard seeds and pulp.

Transfer puree to a 9-in. x 4-in. loaf pan.

Cover with plastic wrap.

Freeze for 1 hour or until edges begin to firm. Stir the mixture very thoroughly with a fork and allow it to freeze for another 30 minutes.

Repeat this process every 30 minutes for 3 to 4 hours until frozen through.