Every year on March 22, World Water Day serves as a reminder of the importance of this fundamental resource for human life. Medically speaking, water is much more than just a comfort fluid - it is at the heart of virtually every physiological function in the body, from the kidneys and brain to thermoregulation, nutrient transport and the elimination of metabolic waste. Yet chronic mild dehydration is one of the most common and least recognized health problems in the adult population of Quebec.
Kidney stones - also known as urinary lithiasis or «kidney stones» - are one of the pathologies most directly linked to inadequate hydration. Their prevalence has doubled over the past thirty years in North America, now affecting around 10 % of the Canadian adult population during their lifetime. Understanding the mechanisms of lithiasis, actual water requirements and prevention strategies can significantly reduce this risk.
The fundamental role of water in the body
Water represents around 60 % of body weight in adults - more in men and muscular people, less in people with a higher proportion of adipose tissue. It plays a role in regulating body temperature through perspiration, transporting nutrients and oxygen to cells, eliminating metabolic waste through the kidneys and intestines, lubricating joints and mucous membranes, supporting enzymatic chemical reactions, and maintaining blood volume and blood pressure.
The kidneys filter around 180 liters of blood per day, producing an average of 1.5 to 2 liters of urine. To do this work efficiently and dilute substances liable to crystallize sufficiently, they need an adequate supply of water. Even mild chronic dehydration - a loss of just 1 to 2 % of body weight in water - is enough to reduce cognitive performance, increase the concentration of urinary substances and predispose to stone formation.
Kidney stones: mechanisms, types and risk factors
Kidney stones form when certain substances dissolved in the urine - calcium, oxalate, urate, phosphate, cystine - become too concentrated and precipitate as crystals that gradually agglomerate. The most common type is the calcium stone - calcium oxalate or calcium phosphate - accounting for around 80 % of cases. Uric acid stones account for around 10 % and are closely linked to a diet rich in animal proteins and certain conditions such as gout. Struvite stones are often associated with recurrent urinary tract infections, and cystine stones with a rare genetic condition.
The main risk factors for urinary lithiasis include low water intake - the number one and most modifiable factor - a diet high in salt and animal protein, excessive dietary oxalate intake in predisposed individuals, a family or personal history of stones, certain medical conditions such as hyperparathyroidism, inflammatory bowel disease and obesity, and certain high-dose medications and supplements such as vitamin C or calcium tablets.
Hydration and stone prevention: how much water should you drink?
The main objective of hydration in kidney stone prevention is to achieve a urine volume of more than 2 to 2.5 liters per day - which generally requires a total fluid intake of 2.5 to 3 liters per day, depending on individual losses (perspiration, climatic conditions, physical activity). A practical indicator of hydration is the color of urine: pale lemon-yellow urine indicates good hydration, dark yellow or amber urine indicates relative dehydration. The aim is to maintain clear urine throughout the day.
It's best to spread your water intake over the whole day, rather than drinking large quantities in a short space of time. Drinking a glass of water on waking, before each meal and before going to bed is a simple strategy. Requirements increase during physical activity, in hot weather or at altitude, during fever, diarrhea or vomiting. People who have already had a kidney stone have a recurrence rate of 50 % at 5 years - rigorous hydration is the most effective preventive measure to reduce this risk.
Nutrition and hydration: beyond pure water
Water intake doesn't just come from drinks: around 20 % of our daily hydration comes from food, especially fruits and vegetables with high water content - cucumbers, lettuce, tomatoes, strawberries, melon and watermelon contain over 90 % of water. Soups, herbal teas and other non-caffeinated drinks also contribute to hydration. Coffee and tea, despite their slight diuretic action, contribute positively to the overall water balance when consumed in moderate quantities.
For the prevention of calcium stones, a diet low in sodium - salt promotes urinary calcium excretion - and moderate in animal protein is recommended. Contrary to popular belief, it is generally not necessary to drastically reduce dietary calcium-rich foods - calcium from dairy products binds oxalate in the digestive tract before it is absorbed, reducing oxaluria. It is calcium supplements taken outside of mealtimes that can increase the risk of stones in certain profiles.
Chronic dehydration: consequences far beyond the kidneys
Mild chronic dehydration - insufficient to trigger the sensation of thirst in many adults, especially the elderly whose thirst mechanism is less sensitive - has measurable consequences on many functions. Cognitively, dehydration of 1-2 % reduces concentration, short-term memory and psychomotor performance. In the digestive system, insufficient hydration contributes to constipation. Cardiovascularly, it increases blood viscosity and the risk of thrombosis. In the urinary tract, it increases the risk of urinary tract infections and stones. On the cutaneous level, it accelerates skin aging and reduces skin elasticity.
Frequently asked questions about hydration and kidney stones in Québec
Is a renal colic attack really as painful as they say?
Yes - renal colic is described by most patients who have experienced it as one of the most intense pains of their lives, often compared to the pain of childbirth. It is caused by the migration of a stone in the ureter, the fine canal that connects the kidney to the bladder. Ureteral contractions to expel the stone generate colicky pain - intense waves of pain - typically in the flank, radiating to the lower abdomen and groin. It is often accompanied by nausea, vomiting and restlessness. It is a medical emergency requiring rapid analgesia and assessment.
Are kidney stones always treated surgically?
No. The vast majority of small stones - less than 5 millimeters in size - expel spontaneously with good hydration, sometimes aided by alpha-blocking drugs that relax the musculature of the ureter. Calculi between 5 and 10 millimetres in size can also be expelled, but require more careful monitoring. Larger stones or those causing obstruction, infection or refractory pain require intervention - extracorporeal shock wave lithotripsy, laser ureteroscopy, or surgery depending on the location and composition of the stone.
Can you tell if you have kidney stones without symptoms?
Yes, many stones are discovered by chance during an ultrasound or CT scan performed for another reason, without the person ever having experienced any symptoms. As long as a stone remains in the kidney without obstructing the flow of urine, it can be asymptomatic for years. A stone becomes symptomatic when it begins to migrate towards the ureter. If you have risk factors or a family history of kidney stones, you may be asked to undergo an imaging test - a kidney ultrasound - during a medical consultation.
Should I stop eating spinach if I've had a kidney stone?
Not necessarily - and not systematically. Spinach is rich in oxalate, which can contribute to the formation of oxalate calcium stones in people with hyperoxaluria or a genetic predisposition. However, the dietary recommendation depends on the type of stone identified by analysis and each patient's urinary metabolic profile. For most people, a varied, well-hydrated diet is more important than categorically avoiding certain foods. A medical consultation with a metabolic assessment can provide personalized recommendations, rather than generic restrictions that may be unnecessary or counterproductive.
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