If your cat is soley eating dry food, they should be making up the difference in moisture by drinking double the amount of water. That is tough to measure, obviously....but general observation should tell you roughly if your cat is compensating. Each cat is going to be different but one eating dry only should be drinking double the amount in water. Check with your vet.
Wet foods already contain a high percentage of water, some nearly 80%, I believe. I don't care for an exclusively wet/exclusively dry diet;I like both to maximize nutritional value (hydration, which affects many other conditions such as constipation, kidneys, crystals/utis, hairballs, etc....dental care, which can also lead to other health issues, etc, etc...)
But many factors can contribute to how much water or how little water a cat is drinking at any given time. It's good to know what is 'typical' for your cat so you could tell your vet and to watch for changes.
I encourage water drinking by having a few different water 'stations', always fresh, and toss a few ice cubes in here and there. One water station is actually a pet water fountain, on the countertop (safe from kids and playing into a cat's preference for vertical space). Keep the bowls clean and fresh.
I have a couple cats who insist on a trickle of tap water a couple times a day as well. I tend to indulge them