6 cups (completely seeded) watermelon fruit,

1 cup water

1/3 cup sugar

1/2 cup lemon juice

Remove as many seeds as you can from the watermelon (see
watermelon.org for the best way to seed a watermelon). Put watermelon
and water in blender and blend until smooth. Pour blended mixture,
through a fine-sieve, into a pitcher, getting out all the juice, and
leaving any pulp and missed seeds behind. Add lemon juice and sugar,
and stir until dissolved. Put pitcher in refrigerator and serve
chilled over ice.