Water, an essential but often underestimated nutrient

Water is the main component of a dog's body. It accounts for approximately 60 to 70% of its body weight and is involved in almost all vital functions.

In particular, it contributes to:

• the regulation of body temperature;
• the transport of nutrients and waste products;
• the maintenance of blood volume;
• enzymatic reactions;
• the proper functioning of organs and tissues.

In animal nutrition, water is considered an essential nutrient. However, when it comes to canine health or nutrition, attention is often paid to proteins, fats, or dietary supplements, much less to the amount of water actually consumed each day.

Yet, good hydration directly influences the functioning of the body and deserves full attention.

Dogs don't always drink when they should

Contrary to what one might think, dogs don't necessarily drink in anticipation.

Thirst primarily appears when their body already detects a lack of water, particularly after an increase in blood osmolality. In other words, they mainly drink in response to an already established need.

A recent review even suggests that many dogs live in a state of mild under-hydration and only compensate when their body demands it.

This phenomenon seems to become more pronounced with age. In senior dogs, the mechanisms that regulate thirst gradually lose efficiency, which increases the risk of dehydration, sometimes without obvious clinical signs.

How much water should a dog drink?

For a healthy adult dog living in a temperate environment, needs are generally estimated at 50 to 60 mL of water per kilogram of body weight per day.

However, this is a guideline and not a fixed value.

Needs increase notably:

• when it's hot;
• after physical exertion;
• during gestation or lactation;
• in case of vomiting or diarrhea;
• during certain diseases, particularly renal or endocrine.

It should not be forgotten that water does not only come from the bowl: a significant portion is also provided by food.

Kibble or wet food: a significant difference

The type of food strongly influences hydration.

Kibble generally contains 8 to 12% water, compared to 75 to 80% for wet food. Fresh foods are most often in between.

This difference is reflected in studies.

Dogs fed a diet richer in water show a higher total water intake, even if they drink less directly from their bowl.

This better hydration leads to more diluted urine, with a decrease in its density and several parameters associated with the risk of formation of certain urinary stones.

Several studies now lead to the same conclusions: increasing the amount of water consumed improves overall body hydration and favorably modifies several urinary parameters.

Good hydration helps the kidneys function normally

The kidneys are directly dependent on the state of hydration.

Studies have shown that dehydration temporarily decreased several parameters of renal function, while they improved after rehydration.

However, it is important to be cautious in interpreting the data.

To date, studies cannot confirm that mild chronic under-hydration alone causes chronic renal failure in a healthy dog. This hypothesis is being studied, but it has not been demonstrated with the same level of evidence as the immediate effects of dehydration on kidney function.

Joints and aging: promising avenues

Water naturally participates in the functioning of cartilage and synovial fluid.

However, available studies do not confirm that mild chronic under-hydration directly worsens osteoarthritis in dogs.

Regarding brain aging, some recent publications suggest that hydration could play a more important role than previously thought in maintaining cognitive functions in older dogs.

These results are encouraging, but still need to be confirmed by additional studies.

How to tell if your dog is properly hydrated?

At home, certain signs may suggest dehydration:

• dry mucous membranes;
• unusual lethargy;
• repeatedly very dark or very concentrated urine;
• a decrease in water intake.

Skin turgor and capillary refill time of the gums are also used by veterinarians, but they alone cannot accurately assess the state of hydration.

In case of vomiting, diarrhea, high temperatures, or if your dog seems abnormally tired, a veterinary consultation is recommended.

How to promote good hydration?

A few simple actions can often naturally increase water intake:

• always leave fresh, clean water available;
• regularly replenish the water in the bowl;
• offer multiple water points in the house or garden;
• moisten kibble;
• include, when appropriate, a portion of wet or fresh food;
• carry water during long walks, sports activities, or very hot days.

These measures are particularly beneficial for elderly dogs, athletic dogs, dogs fed exclusively kibble, or dogs at risk of urinary problems.

In senior, arthritic, or very active dogs, good hydration is an integral part of overall care. It obviously does not replace veterinary treatment or appropriate nutrition, but it contributes to the proper functioning of the body and often deserves more daily attention.

Key takeaways

Hydration is an essential element of dog health, but it often remains underestimated.

The strongest scientific evidence concerns its impact on the urinary tract and kidney function. Other benefits are currently being studied, particularly in elderly dogs, even if some hypotheses still need to be confirmed.

In practice, a few simple measures can make a difference: leaving fresh water available, encouraging dogs that drink little, and adapting their diet when relevant.

Good hydration does not replace veterinary care when necessary, but it is one of the pillars of good health throughout life.

Sources 

1. Sires BS, et al. (2025). Effects of fresh food moisture content on hydration and urinary parameters in healthy adult dogs.
2. Zanghi BM, Gardner CL. (2018). Total water intake affects urine measures of hydration in dogs.
3. Finco DR, et al. (1993). Effects of hydration on renal function measurements in dogs.
4. Guelfi KJ, et al. (2025). Water balance, ageing and hydration in companion dogs: a review.
5. Stevenson AE, et al. (2003). Dietary moisture content influences urine composition and relative supersaturation in dogs.
6. American Animal Hospital Association (AAHA). (2024). Fluid Therapy Guidelines for Dogs and Cats.