Introduction
Commercial dog food sits at opposite ends of a moisture spectrum: dry kibble typically contains around 10% moisture, while wet or fresh-format diets commonly range from roughly 70% to 80% moisture. This difference is large enough to meaningfully change how much water a dog takes in with its food alone, independent of how much it drinks from a bowl. High-moisture diets are frequently recommended for specific clinical goals, supporting hydration, diluting urine to reduce the risk of certain urolith types, and, in some feeding contexts, serving as the format of choice for digestibility and microbiome research. This review examines what the evidence actually supports about high-moisture diets in dogs, and is transparent about where the strongest supporting data currently comes from feline research rather than direct canine trials.
Total Water Intake and Hydration
Sires, Yamka, and Wakshlag (2025) directly examined this question in dogs, demonstrating that feeding fresh food combined with ad libitum water access led dogs to exceed their calculated daily water requirements and measurably affected urine relative supersaturation, a laboratory marker used to estimate the risk of certain crystal and stone types forming in the urinary tract. This is an important, dog-specific data point: it shows that food format, not drinking behavior alone, meaningfully shifts total water intake and downstream urinary chemistry in dogs, providing direct support for high-moisture feeding as a practical hydration strategy rather than a theoretical one.
Complementary evidence comes from feline research, which should be read as mechanistically informative rather than direct canine proof. Buckley, Hawthorne, Colyer, and Stevenson (2011) found that cats fed a diet hydrated to 73.3% moisture produced significantly more dilute urine, with a lower specific gravity and a relative supersaturation for calcium oxalate approaching the undersaturated zone, compared to the same diet at lower moisture levels, despite cats voluntarily drinking less water as dietary moisture increased. Notably, the authors themselves note that the relationship between fluid intake and urinary dilution has also been reported in dogs, which supports treating this as a shared physiological principle across companion carnivores even though the specific experiment was conducted in cats. Kosmal, Shoveller, Gillies, and Armstrong (2026) reinforce this picture with a scoping review of 32 publications spanning 1975 to 2025 on water intake, hydration status, and related health outcomes, concluding that diet format is one of several major factors, alongside protein, amino acid, salt, and osmolyte content, that shape total water consumption; again, this review is centered on cats, and its conclusions should be treated as a strong analogous signal for dogs rather than a substitute for dog-specific data.
Urinary Health and Urolithiasis Risk
The clinical logic connecting high-moisture diets to urinary health rests on dilution: more water intake produces more dilute urine, which lowers the concentration of the minerals that form crystals and stones. The Sires et al. (2025) canine data described above directly support this mechanism in dogs, showing an actual, measured effect on urine relative supersaturation from fresh, high-moisture feeding rather than only a theoretical expectation. This matters clinically because urine relative supersaturation is one of the key laboratory values veterinarians use to estimate a given dog's risk of forming calcium oxalate or struvite stones.
A related consideration is that therapeutic diets formulated to help prevent recurrence of urate urolithiasis, a stone type of particular concern in breeds prone to it and in dogs with certain liver conditions, are frequently formulated as higher-moisture products alongside their purine restriction. Ishii, Scott, Abrahan, Harmon, Colee, Queau, Biourge, Garrett, and Hill (2025) compared the total and individual purine content of commercial maintenance dog foods against therapeutic diets marketed for urate urolithiasis prevention, underscoring that purine content and moisture level are both formulation variables clinicians weigh together, rather than moisture acting as a stand-alone intervention, when managing dogs at risk for this stone type.
Digestive and Microbiome Considerations
High-moisture, canned-format diets are also an established feeding model in canine gastrointestinal research, which speaks to their practical relevance in digestive health contexts even where a study's primary question is not moisture itself. Martini, Oba, Geary, Bauer, Dilger, and Swanson (2025) used fecal inocula from dogs maintained on a canned diet to study the in vitro fermentation characteristics of various dietary fibers, including in dogs concurrently treated with metronidazole, a commonly prescribed antibiotic for gastrointestinal upset. The use of canned-diet-fed dogs as the standard source population in this kind of fermentation research reflects how routinely high-moisture feeding is used in canine digestive studies, though this particular study's findings concern fiber fermentation characteristics rather than a direct comparison of moisture level's effect on digestion.
Where the Evidence Is Strongest, and Where It Is Borrowed
Being direct about the evidence hierarchy here matters. The clearest, most directly applicable canine evidence is the Sires et al. (2025) finding that fresh, high-moisture food plus free water access measurably increases total water intake and shifts urine relative supersaturation in dogs themselves. Much of the surrounding mechanistic support, particularly the detailed dose-response relationship between moisture percentage and urine specific gravity, currently comes from feline studies (Buckley et al., 2011; Kosmal et al., 2026). Cats and dogs are not identical in their thirst-drive regulation or urinary chemistry, so while it is reasonable to expect a broadly similar direction of effect in dogs, given that the underlying physiology of water intake and renal concentration is conserved across companion carnivores, exact magnitudes should not be assumed to transfer directly from the feline literature to dogs.
Why Moisture Content Is Easy to Overlook
Moisture content rarely appears as a headline marketing claim the way protein or grain-free formulation does, yet it is one of the more mechanically direct levers a formulator or owner can pull to influence a dog's total daily water intake. Dogs, like most mammals, do not perfectly compensate for a low-moisture diet by drinking proportionally more from a bowl; the Buckley et al. (2011) feline data illustrate this compensation gap clearly, showing that cats fed higher-moisture diets still ended up with a higher total fluid intake even though they voluntarily drank less water on their own, meaning the food-derived water was not fully offset by reduced drinking. If a broadly similar compensation pattern holds in dogs, and the Sires et al. (2025) canine findings are consistent with that possibility, then simply relying on a dog to drink enough water to make up for a low-moisture diet may not be a safe assumption, particularly for dogs with a lower thirst drive, dental discomfort that discourages drinking, or a preference for food-derived moisture over standing water.
Energy Density and Feeding Volume
A secondary, more compositional consequence of high moisture content is worth noting separately from the hydration and urinary evidence above: because water displaces energy-contributing ingredients on a weight basis, high-moisture foods are necessarily lower in energy density per gram than dry kibble formulated to a similar nutrient profile. A dog eating a canned or fresh-format diet will generally need to consume a larger weight of food to meet the same caloric requirement as on a dry diet, which changes meal volume and, anecdotally, mealtime satisfaction, even though this review did not identify a canine-specific controlled trial isolating moisture content alone, independent of protein or fiber content, as the driver of a measured satiety effect. This is a mechanistic and compositional point rather than a separately verified clinical outcome, and it should not be conflated with the weight-management research on high-protein, high-fiber diets, which tested those two variables specifically rather than moisture.
Practical Takeaways
For dogs at risk of calcium oxalate or struvite urolithiasis, or those who simply drink poorly on their own, high-moisture feeding is a practically supported strategy for increasing total water intake and favorably shifting urine relative supersaturation, based on direct canine data. For dogs at risk of urate urolithiasis specifically, moisture content should be considered alongside purine content rather than as a substitute for a properly purine-restricted formulation. For general digestive health research and formulation, high-moisture diets are a well-established and commonly used feeding format, though this reflects convention and practicality as much as a proven digestive advantage over dry food in every case.
Conclusion
High-moisture diets have a genuine, direct evidentiary basis in dogs for increasing total water intake and improving urinary dilution markers relevant to stone risk, anchored by the Sires et al. (2025) canine study. Much of the finer mechanistic detail supporting this relationship, however, is drawn from feline research and should be treated as strong supporting context rather than dog-specific proof. Purine-related urolithiasis risk requires attention to formulation beyond moisture content alone. As with every category reviewed in this series, the responsible position is to state plainly which claims rest on canine data and which are reasonably extrapolated from a closely related species.
References
Buckley, C. M., Hawthorne, A., Colyer, A., & Stevenson, A. E. (2011). Effect of dietary water intake on urinary output, specific gravity and relative supersaturation for calcium oxalate and struvite in the cat. British Journal of Nutrition, 106(Suppl. 1), S128–S130. https://doi.org/10.1017/S0007114511001875
Ishii, C. S., Scott, K. C., Abrahan, C., Harmon, T. A., Colee, J. C., Queau, Y., Biourge, V., Garrett, T. J., & Hill, R. C. (2025). Comparison of the total and individual purine content of commercial maintenance dog foods and therapeutic dog foods that may be prescribed to prevent urate urolithiasis. BMC Veterinary Research, 21(1), 626. https://doi.org/10.1186/s12917-025-05080-5
Kosmal, P. A. L., Shoveller, A. K., Gillies, G., & Armstrong, L. E. (2026). Diet format, protein, amino acids, salt, and osmolytes, as well as water viscosity, affect water consumption in domestic cats: A scoping review of 32 publications (published from 1975 to 2025) on water intake, hydration status, and related health outcomes. Journal of Animal Science, 104, skaf434. https://doi.org/10.1093/jas/skaf434
Martini, S. E., Oba, P. M., Geary, E. L., Bauer, L. L., Dilger, R. N., & Swanson, K. S. (2025). In vitro fermentation characteristics of dietary fibers using fecal inocula from dogs fed a canned diet and treated with metronidazole. Frontiers in Veterinary Science, 12, 1670624. https://doi.org/10.3389/fvets.2025.1670624
Sires, R., Yamka, R., & Wakshlag, J. (2025). Feeding fresh food and providing water ad libitum is clinically proven to exceed calculated daily water requirements and impact urine relative supersaturation in dogs. Frontiers in Veterinary Science, 12, 1675990. https://doi.org/10.3389/fvets.2025.1675990
