Are you leaving dry kibble out for them to munch on all day? If so, you can just cut out one can meal whenever. As long as you know they're drinking water. My vet told me that canned cat food had almost NO nutritional value at all. It's expensive, stinky and my cats used to poop ALOT more than they do now.

I used to split one can between my cats (8 of them!! ) twice a day and then I cut it back to night only. Now I only give it to them as a treat once in a great while, not as a regular diet. They also get 3/4 of a cup each of dry kibble a day. I also have 3 bowls of filtered water AND a filtered water fountain for them (talk about spoiled!!!)