The theory behind fountains
Dog water fountains use a small pump to keep water circulating and often aerated, and the marketing pitch is straightforward: dogs are drawn to moving water because it reads as fresher, and fresher-seeming water gets sniffed and tasted more often over the course of a day. This lines up with a genuine instinct in many animals, still water in the wild is more likely to be stagnant or contaminated, while moving water usually isn't.
What actually seems to happen in practice
Anecdotal reports from a large number of dog owners are fairly consistent: many dogs do show more interest in a fountain than a static bowl, especially cats living in the same household (fountains are heavily marketed for cats for the same reason) and dogs that have always been picky about drinking. That said, individual response varies a lot, some dogs are indifferent to the fountain and continue drinking from a regular bowl at the same rate as before, and a few are initially startled by the pump noise or movement and need time to get comfortable.
Where a fountain helps the most
A water fountain tends to make the biggest difference for dogs that already drink less than expected, seniors who've become less motivated to seek out water, dogs recovering from an illness where hydration is a priority, or households where the water bowl sits somewhere a dog has to make an effort to visit. It's also genuinely useful in multi-pet homes, since continuous filtration keeps the water fresher for longer between manual top-ups and cleanings, which matters when several animals are drinking from the same source throughout the day.
It's not a fix for a dog that won't drink at all
A fountain can nudge a mildly under-hydrated dog toward drinking more, but a dog that is refusing water altogether, drinking noticeably less than normal, or showing other signs like lethargy or dry gums needs a vet visit rather than a new bowl. Sudden changes in thirst, in either direction, are also worth mentioning to a vet, since they can be an early sign of several medical conditions unrelated to bowl design.
Choosing a fountain that's actually worth it
Look for a model with a replaceable carbon filter, since that's what keeps the water tasting fresh rather than the movement alone, and check the noise level before committing, a fountain too loud for the space it sits in can put a nervous dog off water entirely rather than encouraging it. Capacity matters for larger dogs or multi-dog homes, since a fountain that needs refilling multiple times a day defeats the low-maintenance appeal that made it worth buying in the first place.
Bottom line
Fountains genuinely increase water interest for a meaningful share of dogs, particularly those who were already borderline low drinkers, but they're a nudge rather than a guaranteed fix, and they don't replace paying attention to how much a dog is actually drinking day to day.