Dogs don't realize that we humans find it disgusting when they drink fresh water from a home toilet.  Still it is their drink of choice.  Even kitty likes the coolness of the lavatory, and porcelain is the dog or cats preferred material when it comes to drinking water in a nice cool basin.  That is, they prefer a deep porcelain bowl that maintains cold to cool aerated water, better known as the toilet,commode,or some other French word.  They know from just sniffing the water bowl whether or not you have lately provided fresh water.  Dogs do not like the taste of water that has stagnated and picked up the taste of plastic,etc.  In this case, your dog may turn to the toilet.  Your cat may run away from home.

Don't fret if you find your dog or cat does indeed prefer to drink his water from a commode. It is nothing to be ashamed of; it happens to the best of us!  Simply keep the toilet lid closed (though some dogs have learned to open the lid), or just keep the bathroom door closed.   If chemicals are maintained in your toilet water, it is a necessity to close the bathroom door...  Another solution, to keep your dog or cat from drinking toilet water, is to buy a porcelain or ceramic drinking bowl.  The key to a ceramic bowl is to keep the water fresh and to drop in a few ice cubes.  As for felines, a few people are known to provide champaigne glasses in their bathrooms for the cat's drinking water-yet they know they had better keep the water fresh!  

It is good that humans have come so far in figuring out the mystery of the dogs preference for drinking water from a toilet.  We face complex decisions ourselves in deciding what is the best way to drink our own water.  There are even people who could be described as "water snobs".  There is the current trend to drink tap water, filtered tap water,commercial filtered tap water, and mineral water from deep inside the earth that has never seen the light of day in thousands of years. To be sure, each viewpoint and prefernce maintains its own drinking snobs.  So dogs too have their preferences...clean fresh water!