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.

Ensuring cats consume sufficient water to maintain their health is a common concern for cat owners. Despite the connection between water intake and animal health, the optimal water intake levels for cats are poorly understood. The present scoping review aimed to determine the extent to which cat hydration research has been conducted, the reported average daily water intake of cats, and whether their water intake requirements have been identified. Online databases were used to identify papers published between 1975 and 2025, from which we selected 32 publications written in English that provided the water intake of cats as an outcome variable. Across an assessment of five groups of healthy domestic cats, 23 to 51 mL/kg BW of total water was consumed daily. A further eight papers reported that cats consumed 70 to 293 mL of water daily. Urine specific gravity (USG) was the most reported physiological biomarker used to assess a cat's hydration status and is used to assist in the diagnosis of diabetes insipidus, glomerulonephritis, pyelonephritis, adrenal insufficiency, hepatic disease, and congestive heart failure. USG was frequently measured in conjunction with urine pH, volume (or output), calcium oxalate, struvite, and/or serum biochemistry and a complete blood count to evaluate gross kidney function. The water intake of cats was highly variable within and across studies. Still, it was influenced by factors such as diet format (wet or dry), dietary protein or amino acid content, salt, osmolytes, and water viscosity. The water intake of cats was not affected by fat content or water source type (static or flowing). Healthy cats that consumed 42 to 51 mL/kg BW of total water daily often had a USG <1.035, and this was achieved only when consuming a wet diet or a dry diet with supplemented nutrient-enriched water. Except for those supplemented with nutrient-enriched water, cats on a dry diet had lower TWI and higher USG, suggesting they may be at greater risk of developing feline lower urinary disease, including crystalluria and urolithiasis. Although the minimum water requirement before cats become at a greater risk of developing urinary or renal disease remains unknown, these results provide some evidence of the minimum water intake required for optimal hydration. If not consumed, these cats would likely benefit from a wet, semi-moist, or fresh (high-moisture) diet.