Why do cats prefer dirty water? The internet has been incredibly educational regarding cat welfare and therefore I would expect most people to know the answer to this question but for the sake of clarity I’ll discuss it in any case.

Chemicals
We know that there are chemicals in tap water. It is often chlorinated strongly enough to be able to smell the chlorine. A websites states that the full constituents of tap water are:
- Chlorine.
- Fluorine compounds.
- Trihalomethanes (THMs)
- Salts of: arsenic, radium, aluminum, copper, lead, mercury, cadmium and barium.
- Hormones.
- Nitrates.
- Pesticides.
Are you surprised that some cats don’t like it that much?
There is another source of chemicals which is the detergent that people use when washing cat bowls in dishwashers. It is possible and probably likely that some detergent is left on the bowl.
As the cat’s nose is very sensitive they quickly detect these chemicals and for some cats it is intolerable. Water allows the chemical smells to become noticeable but the odor of cat food probably masks them. In short, tap water is too sanitized and therefore an individual cat may prefer a dirty puddle of water in the garden. It does depend on the cat.
There may be microbes and rotting vegetation in water puddle but it doesn’t put off a domestic cat because they are natural. They may even like the flavor! One danger of a puddle of water in the back garden if that it may contain chemicals as well. I am thinking of garden pesticides and weedkillers. I am not a believer in the use of garden products such as weedkillers, pesticides and lawn enhancers when cats are around. All of them can hurt a cat in my opinion.
Safe option
Perhaps the safe option is to make sure that the water bowl with which you provide your cat is rinsed efficiently of traces of detergent. Also, it may help to allow the chemicals to dissipate in the water by allowing it to stand for some time before offering it to your cat.
The cat is very sensitive to chemical contamination. We know how impossibly difficult it is to encourage a cat to eat food that has a pill hidden in it. They can pick up the smell of the pill or the taste of it incredibly quickly.
Thanks Jane. I believe that some domestic cats have references for the type of bowl that they drink from in terms of what it is made of and its appearance. This may be a visual thing or odor. It is definitely worth trying different bowls to encourage drinking.