In a medium saucepan, combine the chopped rhubarb, water, and sugar. Bring to a boil over medium heat, stirring occasionally until the rhubarb breaks down, about 10 minutes.

After cooking, remove the saucepan from heat and let it cool slightly. Pour the mixture through a strainer into a bowl, discarding the solids to get a smooth rhubarb syrup.

Allow the rhubarb syrup to cool to room temperature, then refrigerate it until thoroughly chilled.

In a blender, combine the chilled rhubarb syrup, ice cubes, and lemon juice. Blend until smooth and slushy.

Taste the slush and adjust sweetness if necessary. Add more sugar or sweetener, blending again if you do.

Pour the slush into glasses. For a fun presentation, garnish with a slice of lemon or a sprig of mint.

Sip and savor the delightful tartness of the rhubarb slush on a hot day.

If you have any slush left, store it in an airtight container in the freezer. Stir before serving again.