A 10 pound cat only needs 7-9 ounces of water a day. Most cats will only drink 2-4 ounces. Which means they get anywhere from 50-80% of water from their food. I figure going with the lower end of water drinking, 2 ounces, and the upper need, 9 ounces, means the get roughly 75% of water from food ideally. Assuming that the higher water drinkers are probably on a dry diet and drinking more because they are getting less from food.I do think it's likely more natural for them to get most of their liquid in food. When we brought her home she was drinking a ton, but it turns out that was a symptom of the coccidia (diarrhea and dehydration and all that) and once we got that under control her drinking seemed to slow down to a normal amount.
My Cat Won’t Drink: How Much Water Cats Need & Dehydration Prevention
How Much Water Should a Cat Drink?
Paying attention to your cats water intake can help you know if they are getting enough, or like you found out, if they are sick and drinking more as a result.