Possibly not, if you are on a strictly water fast. If you drink adequate amounts of water, but are not ingesting any solid foods, soups, or juices, your system will eliminate toxins into your colon, but may not result in a BM.
It's a good idea during a Water Fast to take periodic cleansing enemas (preferably once or twice daily), to assist in the release of toxins and whatever waste has accumulated from the colon.