Watermelon Juice

I know I already posted this picture, but I didn't include the recipe.
My sister-in-law, Stephanie made this for all of us on the 4th of July. The kids loved them, and some of the adults added a little rum to ours to spice them up a bit. Next time I make it, I will probably blend it with some ice for a slushy kind of texture (probably do the rum thing again, too).

6 c. of cubed watermelon, blended
1 c. sugar
1/2 c. water
1/2 c. pineapple juice
one can frozen lemonade concentrate, thawed

In a small saucepan, combine the water and sugar and bring to a rolling boil, and simmer for 1 minute.
Strain the watermelon puree (I use a collander lined with coffee filters). Blend together the sugar mixture, watermelon, pineapple juice, and lemonade.
Serve over ice.