Do they have access to other water? A fish tank, toilet, shower, sink? Is the water bowl clean? Do they go outside, and if so, could they be getting water from somewhere else?

Cats were originally desert animals, which is why their urine can become so strong and concentrated (and stinky!). But since this is hard on their kidneys, it is a good idea to get them to drink water.

Maybe try a different bowl, or a couple of bowls? You could also turn on the sink and see if they drink from that. (obviously you can't leave that on all day but it might get them to get a good drink at least once or twice a day.)

When the weather is really hot, I turn on an outside sprinkler to just burble out a little bit of water and my Joxer loves to drink water this way.