How effective is water fasting in losing weight?

Can you answer Amelie’s question about Weight Loss?:

I am around 5′6 and weigh 160 lbs. I would really like to lose weight fast- potentially fifteen or twenty pounds. I have heard water fasting is both good for losing weight, and is also beneficial to gastro-intestinal health.

Is water fasting as effective as it is said to be?

Tips For Fast Weight Loss