When your levels are running high, your body will try to flush excess sugar out of your blood through the urine. As a result, your body will need more fluids to rehydrate itself. Drinking water can help the body with flushing out some of the glucose in the blood. Just a word of caution to be sensible with drinking water; water intoxication (which can result in death) is possible if a number of litres water are drunk in a short space of time. This is rare and quite difficult to manage but it pays to be aware of this.
To see this working, head to your live site.