Why cats under-drink by design
The biggest lever is the food bowl, not the water bowl
The most reliable way to raise a cat's water intake doesn't involve persuading the cat to drink at all: feed moisture. Wet food and fresh food carry most of their weight as water - closer to prey than any kibble can be - so shifting some or all of the diet toward high-moisture food raises intake automatically, no cooperation required.
Even partial moves count: a wet or fresh meal alongside dry feeding, or a spoonful of plain water stirred into wet food for cats that tolerate it. This is, honestly, one of the stronger practical arguments for the fresh and wet categories.
Make water instinct-friendly
For the drinking your cat does do, work with instincts instead of against them. Many cats prefer moving water - it reads as fresher - which is why fountains often succeed where bowls fail; if you try one, keep it clean, since a slimy fountain defeats the point.
Use wide, shallow bowls (some cats dislike whisker contact with bowl walls), refresh water daily, and place stations away from both food and litter - cats instinctively distrust water next to either. In multi-cat homes, several stations in different rooms beat one contested bowl.
Know what changes mean
Two cautions keep this project safe. First, flavor experiments should stay plain: no seasoned broths or anything containing onion or garlic, which are toxic to cats - if you flavor water at all, it should be something unseasoned and cat-safe.
Second, watch the direction of change: you're nudging intake up from a healthy baseline, but a cat that spontaneously starts drinking dramatically more (or urinating much more) may be showing early signs of kidney disease, diabetes or thyroid trouble - that's a prompt vet visit, not a win. Sudden drops in drinking or eating deserve the same call.