Water in your cat diet: dry or wet food?
In this article, I am going to talk about an element of a cat's diet which is essential and far too often forgotten: water. I am also going to talk about moisture in food, as it’s something that must be taken into consideration when talking about water intake for cats.
Water
Water is often considered the most important nutrient. It is one of the largest constituents of a cat's body: around 60 to 80% of a cat's body weight is water.
Water has several roles, such as the transport of nutrients, the regulation of the body temperature and it is an essential component of the digestion process. A deficit of only 15% of body water can lead to death. So, as you may expect, water has quite an important role in a cat's diet!
The water in the body is mainly lost in the urine, but also from feces, through respiration and sweating. This water, lost during normal bodily functions, needs to be replaced. So, what are the sources of water for your cats?
There are three sources for body water: water present in the food, voluntary water intake (drinking), and metabolic water. Metabolic water is the water produced in your cat's body during the metabolism of the nutrients, and it accounts for around 5-10% of the animal's water intake.
The amount of water coming from the diet and from drinking depends on the type of diet: I will talk about this more in detail in the next paragraphs.
The estimated average water consumption of cats is between 10 to 45ml of water per kilogram (or 0.3 to 1.6 fl oz per 35 oz) of body weight, per day. But these values depend on many parameters, such as the environment temperature and humidity, the cat's level of activity, the physiology of the animal, and the diet.
Water quality
Water quality is important, as a cat will be more inclined to drink if the water is of good quality. Here are some criteria to determine if the water is of good quality or not:
The water should be fresh, odorless, and tasteless
Neutral pH (> 6.5 and < 8.5)
The total mineral content should be < 0.5 g per liter
The water should be free of heavy metals, pesticides, herbicides and should contain low levels of nitrates and nitrites.
Finally, it should be free of bacterial contamination.
A piece of advice to be sure to provide clean water is to use bowls made of ceramic or stainless steel instead of plastic, as they are more hygienic and easier to clean. Be careful about the quality of your tap water, check with your water department to verify that the water is drinkable and its quality.
Finally, be sure to change the water available to your cat every day and to clean their water bowl regularly.
Water & diet: don’t feed a dry diet!
Now let’s talk about the elephant in the room: the influence of the diet on water intake.
Cats’ diets can generally fit into two categories: dry and wet.
Dry diets, like kibbles or freeze-dried raw, have a low moisture content, generally 6% to 10%.
Wet diets, like canned food and raw food, which have a high moisture content, generally have a moisture content of around 75%.
As I mentioned before, part of the water intake comes from the food. So, in a dry diet, the water intake coming from food will be low and the cat will need to drink more water. On the contrary, if the diet is wet, the water intake from the food will be high and the cat needs to drink less water.
In theory, the end result which is the global water intake of the cat would be the same, no matter if the diet is dry or wet.
However, this is not what happens in reality: cats are originally animals coming from the desert: the ancestor of the domestic cat is the African wildcat (Felis lybica). In nature, cats hunt small prey containing 70-75% moisture and get most of their water intake from their prey. In fact, cats can survive without drinking if they are fed a diet containing more than 70% moisture [1]. This can be seen when you feed your cat a raw diet: they may almost not drink any water. This adaptation to the desert habitat comes with a greater ability to concentrate their urine when compared to dogs, in order to retain a maximum of water and to have a low thirst drive. While dogs start drinking after losing around 4% of their body water, cats will not voluntarily drink until they lose 8% of body water [2].
So, when a cat is fed a dry diet, even if it will drink more than if it was fed a wet diet, it will still not drink enough to reach the total water intake of a cat fed a wet diet [3][4][5][6][7].
To give you an idea of the difference in water intake between a dry and a wet diet, a study showed that even if the cats fed a dry diet were drinking 6 times more than cats fed a wet diet, their overall water intake was still 30% less than the cats fed a wet diet [8]. There is a scientific consensus on this subject and several studies from the ’80s to today have shown that the water intake of a cat eating a wet diet is higher than the one of a cat eating dry food [8].
The issues
Now the question is: is this actually a problem for cats? It is! In fact, cats fed a dry diet can end up being less hydrated, which can directly affect their health [3]. Cats fed a dry diet have higher risks to develop urinary tract disorders such as urinary stones (struvite and calcium oxalate), urinary infections, and idiopathic cystitis [4][8][9][10][11][12][13][14][15][16][17]. This is explained by the fact that as cats have a lower water intake, they also have a lower urine volume and less micturition. The urine, as a result, is also more concentrated, which may lead to the development of urinary stones. Wet diets not only prevent urinary issues, but they also prevent recidivist cases of urinary diseases [4][8][9]. Similarly, wet diets are recommended for the treatment of many diseases, such as chronic kidney issues.
Other benefits of high-moisture diets
Recent studies have also shown that cats eating a high-moisture diet have higher energy levels than cats consuming dry food [3][18][19].
Diets containing high levels of water have a lower caloric density, which means that in 100 g of kibbles there are many more calories than in the same quantity of canned or raw food. This is simply explained by the fact that canned or raw food is composed of 70% water, which doesn’t bring any calories. That’s why high moisture diets are recommended also for preventing obesity and for weight loss programs [19][20]. This is not something to neglect when 1 out of 3 cats is obese, and when this figure keeps growing.
How to make your cat drink more?
Feed as much wet as possible
So, how to make your cat drink more? The simple answer to this is not to feed any dry food and, instead, feed a raw or a canned diet. If you decide to feed a canned diet, be sure that it’s complete and balanced (as opposed to complementary).
If, for whatever reason, it's not possible to provide your cat with an entirely wet diet, try to reduce the quantity of dry food in the diet of your cat as much as possible and to partially feed canned and raw.
Rehydrating kibbles
Another tip that, however, may not work with most cat eating kibbles (but that may be worth trying!) is to rehydrate the kibbles by letting them absorb water for 10 minutes. The goal is that they keep their shape but that the moisture content increases. However, as they can be very picky, most cats will refuse to eat rehydrated kibbles. One thing to keep in mind is that water favors bacteria growth, so rehydrated kibbles shouldn’t be left out for too long.
Water fountains
Water fountains could increase water consumption for some cats. Water fountains recommendations, however, are mainly based on anecdotal rather than sound evidence: to the best of my knowledge, until now no study proved this effect. However, it seems that some cats may have indeed a preference for flowing water, as opposed to still water in bowls [21][22].
To wrap up, water is an important nutrient that is often overlooked, especially considering the fact that cats are not made to eat a dry diet. If you have the means, a high-moisture diet can increase the water intake of your cat and its overall health.
Sources
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