Zest the orange and mince the zest.

Juice the orange.

Remove string from the rhubarb.

Cut the rhubarb into roughly 2-inch lengths.

Combine the rhubarb, sugar, 4 cups of water, orange juice, and half of the minced zest in a saucepan.

Bring the mixture to a boil.

Wrap and refrigerate the remaining zest.

Reduce heat to medium and cook for 10 to 15 minutes, or until the rhubarb begins to fall apart.

Chill the soup thoroughly.

If you are in a hurry, pour the mixture into a large bowl and set that bowl in an even larger bowl filled with ice water.

When cool, whisk briefly to break up the rhubarb.

Add the reserved zest at the same time you are whisking.

Serve cold with sour cream or any of the listed alternatives.