"Many dogs and cats love to drink from the toilet. Thirsty dogs and cats lap up the water with vigor simply because it is cool and accessible. It's much easier for the pet owner who just has to leave the lid open and avoids having to fill up an additional dish with water.
The problem is, toilets are full of bacteria and that bacteria can potentially cause your dog or cat to get sick. In addition, toilet cleaner is extremely toxic to both cats and dogs and there is often cleaning residue in the toilet. Finally, depending on the traces of what was in the toilet, drinking from it can give your pet horrible breath.
Don't let your pets drink from the toilet. Always keep the toilet lid down, and provide cats and dogs with fresh drinkable water each day."