Yes, Bragg also says drink when you are thirsty only, unfortunately most people are completely out of touch with how dehydrated they are, so 10 glasses is a nice number to shoot for. If you drink water and you are "full" and don't want to drink anymore, obviously you should stop there.
Personally, I drink more than 10 glasses of water a day when fasting, so it depends on the person. And maybe the size of the glass. :)