Why moisture content matters
Cats have been living with us for a long time—more than 9000 years according to some sources. Domestication occurred in the arid climates of Egypt and the middle east, and since that time, house cats have retained a number of desert-dwelling behaviors.
Among the most obvious of these personality traits is the way cats deal with water. In general, our feline friends can be pretty skeptical of still water, and will usually prefer to drink from a running source such as a dripping tap. Most cats’ favorite method of hydration, however, is to take in moisture through the food they eat.
In the wild, a typical prey animal such as a field mouse will have a moisture content of somewhere between 70 and 85 percent. Therefore, by consuming the whole prey animal, cats are able to satisfy a significant amount of their hydration needs. Hydrating by consuming (living) foods helps cats to keep away from possible waterborne contaminants, which are often more of a threat in hot climates.
Wet cat food does a pretty good job of recreating the moisture content of whole prey, with can foods tending to come in between 70 and 80 percent moisture, and pouch or tray foods at 75 and 85. When it comes to dry foods, however, production processes leave kibbles with a measly 5 to 15 percent moisture.
While this helps extend the shelf life of dry food, it leaves cats with a product that’s unfamiliar on a biological level. Having a ready supply of fresh water kept next to their food dish will help them to replace some lost liquids through hydration, but the truth is that cats only eating dry food without added moisture (by mixing or mashing kibble) are at a higher risk of dehydration-related disorders, such as kidney conditions and diabetes.