|Running water is naturally enticing |
to many cats and is one way to get
cats to drink more water
Water serves many physiological functions: it transports nutrients and oxygen through the blood stream and into the cells, moisturizes the air in the lungs, regulates body temperature, protects and moisturizes the joints and internal organs, and helps eliminate waste products of metabolism through the kidneys and gastrointestinal tract.
Cats Do Not Naturally Drink Much Water
Cats do not normally need to drink very much water. Cats have evolved to obtain their water requirements almost entirely on the moisture content in their food. In the wild, cats obtain most of their water from freshly killed prey (e.g., small rodents, birds, amphibians, and insects), all of which contain about 70 to 75 percent water (3-7). Cats can do well for long periods without drinking any water when receiving canned food containing 67 to 73 percent water (8, 9); however, they will become dehydrated when the water content of the food drops to less than 61 percent (9). Therefore, normal cats eating rodents or birds or house cats eating canned-only foods may obtain enough water in their diets so that extra drinking water may not always be needed (2,10).
It's very important to realize that domestic cats have a diminished "thirst drive" and ideally will derive most of their daily water intake from the moisture contained in their food. In this respect, control of water balance in cats differs markedly from that of dogs and most other animals. When dehydrated, cats are slower to initiate drinking or to drink enough for complete rehydration — one study found that dehydrated dogs will drink enough to replenish 6 percent of their body weight in an hour compared to the 24 hours it takes for dehydrated cats (11).
In response to changes in the water content of food, cats adjust their voluntary water intake less precisely and less rapidly than do dogs. Similarly, their compensatory drinking response to dehydration induced by higher environmental temperatures or concurrent disease is less effective than it is in dogs.
How Much Water Does a Cat Need to Drink?
The amount of water drunk by an individual cat depends on a variety of factors, including the cat's size and activity, the season, and whether the cat's diet includes wet food or dry cat food only (2,10,12). Factors such as high heat, exercise, or lactation can double or triple the amount a cat drinks. And, of course, diseases such as hyperthyroidism, kidney disease, and diabetes will all greatly increase a cat's daily water requirements (I'll talk more about water and hydration in these cats in my next post).
So how much should a cat drink? A normal cat’s daily water requirement ranges from 5 to 10 fluid ounces per day (or an average of 60 ml/kg/day). Cats eating canned food will receive much of their daily water needs from its food, since canned food is about 70 to 80 percent water. In contrast, dry food is only 7 to 10 percent water. Normal cats eating canned food may need to drink less than 1 ounce of additional water per day, whereas a cat consuming only a dry diet may need to drink over 7 ounces per day to stay hydrated. This higher amount of water can be difficult to achieve because cats are not prone by nature to drink large amounts of water.
Will Type of Food (Dry vs. Canned) Affect the Amount of Water a Cat Drinks?
A cat consuming a predominantly dry food diet will drink more water than a cat consuming a canned food diet. But in the end, when water from all sources is added together (moisture in their diet plus the water they drink), the cat on dry food consumes about half the amount of water required for adequate hydration compared to a cat eating canned food (2, 13).
Put another way, when cats are fed only dry food, they do increase the amount of water drunk but not nearly enough to fully compensate. In one study (12), cats consuming a dry food diet containing 10% moisture with free access to drinking water had an average daily urine volume of 60 milliliters (or 2 fluid ounces). This urine volume almost doubled when the cats were then fed a canned diet containing 75 percent moisture.
Calculating the Volume of Water Provided by the Cat’s Diet
The moisture content of all cat food (both canned and dry) is listed on the product label as part of the Guaranteed Analysis (14). Canned diets usually contain about 75% moisture, so for every 100 grams of food fed, 75 grams (which equals 75 ml) is water. Dry foods, on the other hand, contain only about 10% moisture, so for every 100 grams of food fed, 10 ml if water.
The weight of a standard, larger can of cat food is 5.5 ounces (156 grams). If the moisture content of the food is listed as 78 percent max and the cat eats the entire can of food, he or she would be ingesting approximately 120 ml of water from the food (156 gm X 0.78 = 121.68 ml). Again, if the same cat at 156 grams of a dry food containing 10% moisture, that would provide only 15.6 ml of water.
The weight of a standard, smaller can of cat food is 3 ounces (85 grams). If the moisture content of the food is again listed as 78 percent max and the cat eats the entire can of food, he or she would be ingesting approximately 65 ml of water from the food (85 gm X 0.78 = 66.3 ml). Again, if the same cat ate 85 grams of a dry food containing 10% moisture, that would provide only 8.5 ml of water.
Water Requirements in Cats with Hyperthyroidism
Although water is certainly important for clinically normal cats, it is absolutely essential in maintaining and restoring health in sick cats, and that certainly includes cats with hyperthyroidism. To that end, I'll address the special water needs of hyperthyroid cats in my next post.
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- Food and Drug Administration website. Pet food labels—general.