The amount of water a cat should drink should be about 2.5 times its daily intake of food. As an example, a cat should drink about 10 ounces of water if it eats four ounces of dry food in a day.
A cat can become dehydrated in only a few hours on a hot day if fresh water is unavailable. Serious illness can result from a body water loss of only 10 percent. A factor, such as lactation, increased physical activity or an excessively hot day can cause the daily need for water to increase by as much as two or three times the amount normally needed. Animals are not at risk if they drink too much water, but not having enough could become harmful.