There are breeds of cats with an affinity for water. There have been reports from rec.pets.cats readers about cats getting into showers with them; other anecdotes have been very entertaining to read.
Most cats, whether or not they like to get wet, will be fascinated with watching water drip out of faucets or drain out of tubs, sinks, and toilets.
Reports of cats drinking from the bottom of the shower, from the sink and other unlikely places are common. Some cats can be fussy about water; they seem to like it as fresh as possible, preferably still moving. You may be able to stop some of this behavior by changing the cat's water every day and moving it some distance away from the food dish. In general this habit will not hurt your cat, however unpleasant it may look to you. Toilet water drinking *should* be discouraged, but this is easily done by leaving the lid down.