According to Healthy Holistic Living, Keurigs are not able to be drained and dried entirely after use. This basically means that there's a potential for mold and bacteria where the water has been sitting for long periods of time.
The truth of the matter is that Keurig machines (and similar products) can become moldy if not regularly cleaned. Coffee makers should be cleaned every time you use them, or at least once a day.
You want a burst of energy not a blast of poison so wash your machine thoroughly or perhaps think of a different system. :-)