Water inside Carburetor?

Today, as I was going to my office per my daily routine, my bike slow down suddenly it breaks down in the middle of the road. I was confused as I was thinking maybe air filter needs a cleaning, so I went up to the repairing store to clean my bike air filter. I continued my ride to office as I was about to be late, as I ride a few distances I got the same break down in my engine. Finally, I have to check my carburetor. so, the mechanic checks the carburetor and found that there was water inside. I wonder how water gets in there.
Any Idea?