Cats don't like having their water next to their food; if you separate the food and water dishes to different rooms, a lot of times they get more enthusiastic about the water in the dish.
I have a cat who absolutely has to drink from the dripping bath tub faucet. If it isn't dripping, she will complain outside my door until I turn it on for her.
Cats have a natural instinct to avoid stagnant water. Freshly fallen rainwater does it for them sometimes, but a water dish will always be an object of suspicion.