Keurigs dont have wate pumps, they use air pressure and vacuum to move water around. These vales in Keurigs were originally designed for air and will eventually leak and damage your Keurig. Apparently this is a common issue and also affects the Cuisinart Keurig coffee maker.
You will know when your Keurig starts to fail because it can no longer fill a normal cup of coffee
To fix this replace the valves in your Keurig.
I purchased my replacement valves from here: