Tap water contains minerals that accumulate inside a coffee maker. These minerals might include lime, and too much lime can have an adverse effect on the performance of the machine. Certain Keurig coffee maker models have a light that tells you when you need to de-lime the machine. In any case, a good rule to follow is to de-lime the machine once every six months. For hard-water areas, de-lime the machine once every three months.
Empty the Keurig water reservoir into a sink. If the reservoir detaches from the body of the machine, reattach it afterward.
Fill the water reservoir with undiluted vinegar.
Place a ceramic mug on the drip tray beneath the brew head. Turn the Keurig machine on to let it heat. Do not add a K-Cup -- the Keurig pods containing ground coffee -- to the machine during the process of de-liming.
Press the brewing button to fill the ceramic coffee mug.
Remove the filled mug from the brew tray and pour the vinegar back into the water reservoir.
Repeat the brewing process three more times, emptying the contents of the mug back into the Keurig coffee machine each time.
Keep the machine turned on for four hours. After four hours, run the brew cycle four more times.
Pour the vinegar from the last brew cycle into the sink. Place the mug back beneath the brew head, then run the brewing option until all vinegar is drained from the machine.
Fill the reservoir with water. Run four more brewing cycles to dispense any vinegar residue from the machine.