I’m primarily thinking of domestic cats in writing this article but, of course, it applies to all animals. Ethylene glycol (antifreeze) is sometimes (hopefully rarely) added to water in fountains to prevent freezing. Cats love flowing water. Domestic cats are also attracted to antifreeze because it is naturally sweet. I’ve used the word “attracted”. Perhaps the better explanation is that cats are not deterred from drinking antifreeze because not all antifreeze has a bittering agent added. That’s why sometimes cats simply lick it off the road if it has leaked out of a vehicle or been deliberately left on the ground. It kills cats by damaging their kidneys. It’s almost certain death.
Adding antifreeze to a fountain to stop the water freezing and damaging the fountain in winter is not a good idea, period. Even if the antifreeze that you add has a bittering agent. The advice is to simply dismantle the fountain and place it inside at a temperature which is guaranteed to be above freezing all the time. If it’s not you have to thoroughly dry the entire fountain including the internal working parts before putting it into storage.
Any moisture in the fountain when it freezes expands, damaging the product. Most outdoor fountains are made of concrete or pottery. If moisture gets into these substances it can cause cracks.
I think the underlying advice is that a garden or backyard fountain should not be left out (if that is possible) during the winter unless you can guarantee the winter months are above freezing. If the fountain is fixed to the ground it seems to me that you are going to have to remove all the water from it and then it should be covered during the winter with a tarpaulin or some other protective, waterproof material.
The bottom line is that any chemical antifreeze is unsuitable for a garden fountain.
Are there substitutes to antifreeze to prevent water in a fountain freezing? There are many substitutes but some can damage the pump in the fountain and no doubt some or all will be potentially poisonous to domestic and wild animals. Personally I would not add anything to water in a fountain to prevent it freezing. It’s just not going to work in terms of animal welfare.
SOME MORE ON TOXIC TO CATS: