Many of us have that wonderful invention from Keurig: the one cup at a time beverage maker! Since it is used so often, it needs to be cleaned! To do so add 2 tablespoons of citric acid powder (you can find this in the baking aisle) into the reservoir, then fill with water, and run through a brew cycle without a K-cup. The acidity will break down the limescale. Refill with water and run a few more cycles without the K-cup so you can rid any citrus taste.