How much water you actually need in a hot climate

Where did the eight-glasses rule come from and is it accurate?

Almost everyone has heard the advice to drink eight glasses of water daily. Far fewer people know where this figure originated or why it is far less precise than it sounds. The original source was a 1945 United States National Research Council recommendation estimating that an adult needs roughly 2.5 litres of water daily. The same recommendation noted that most of this comes from food, not from drinking water alone. That second sentence was quietly forgotten, and the drinking-water number remained.

The amount you actually need depends on your age, sex, body weight, physical activity level, ambient temperature, humidity and what you eat. A person sitting in a 22-degree air-conditioned office has very different needs from a construction worker spending eight hours under a 42-degree Kuwaiti or Syrian summer sun. Treating both with the same number is not useful.

For hot climates where most readers of this site live, a broadly useful estimate is 3 to 4 litres daily for an average physically active adult man and 2.5 to 3 litres for a woman. These are approximations. The practical indicator that is more reliable than any number is urine colour, which is discussed in the next section.

Urine colour: the most useful daily hydration check

Rather than counting glasses, checking your urine colour gives you a faster, more direct reading of your hydration status. This is not folk wisdom but a scientifically validated assessment method. Kavouras described it in Current Opinion in Clinical Nutrition and Metabolic Care in 2002 as a practical tool for estimating hydration when laboratory testing is not available. Armstrong and colleagues validated urine colour scales against urinary osmolality in 1994, establishing the scientific basis for their use.

Very pale, almost clear urine suggests you may be overdrinking, which is uncommon in hot climates but possible with certain medications. Pale yellow, similar to light lemonade, indicates good hydration and is the target. Dark yellow or amber urine indicates meaningful dehydration and you should drink water now rather than waiting for your next scheduled glass. Brown or orange-brown urine is a more serious signal and may indicate severe dehydration or kidney involvement, particularly if accompanied by pain or reduced urine output.

An important qualification: certain foods and medications alter urine colour in ways unrelated to hydration. Beetroot can produce pink or reddish urine, vitamin B2 produces a vivid yellow, and some antibiotics and blood pressure medications cause colour changes. If you notice a sudden colour change accompanied by other symptoms, speak to a doctor rather than assuming it is just hydration.

Dehydration signs that people commonly miss

Thirst is not the first sign of dehydration. By the time you feel noticeably thirsty, your body has already lost enough fluid to begin affecting its functions. This delay between actual dehydration and the sensation of thirst increases with age, making older adults substantially more vulnerable to silent dehydration in hot weather.

Mild to moderate dehydration commonly produces: headache, particularly in the middle and back of the head, fatigue and reduced concentration, dry mouth and throat, reduced urine output with darker colour, and mild dizziness when standing up quickly. Many people attribute these symptoms to other causes without considering hydration first.

Signs of severe dehydration include: pronounced dizziness when standing, confusion or mental cloudiness, rapid breathing, very concentrated urine or no urine output for many hours, and rapid heart rate. These warrant medical attention and not simply drinking water at home.

Outdoor workers: a high-risk group

Workers who spend their days outdoors in the regional sun, including those in construction, agriculture, sanitation and road maintenance, face dehydration and heat illness risk disproportionately. A study published in the Annals of Work Exposures and Health in 2020 followed construction workers in Saudi Arabia, measuring their skin temperature, hydration status and heat strain indicators during summer. The findings showed workers operating in conditions of extreme heat strain, with a significant proportion showing poor hydration throughout the working day.

An earlier study published in the Annals of Occupational Hygiene in 2010 followed expatriate manual workers during summer in the Gulf region and found that the majority began their working day already partially dehydrated. This means that dehydration accumulates before workers even reach the worksite, and that drinking during working hours alone is insufficient to recover lost fluid.

The practical guidance for these workers and their supervisors: drink at least 500 ml of water before starting work, roughly 500 ml per hour during sun exposure, and more when wearing heavy protective clothing or working in high humidity. Cold water is absorbed slightly more quickly than room-temperature water and helps reduce core body temperature, making it the better choice in these conditions.

Why sugary drinks fail as water replacements

Many people in the Arab world replace a significant portion of their daily water with carbonated drinks, sweetened juices or energy drinks, assuming that fluid is fluid regardless of what it contains. This assumption has real consequences for hydration quality.

Drinks with high sugar content have a higher osmolality than blood, meaning they contain a higher concentration of dissolved particles. When a high-osmolality drink enters the intestine, the body sometimes draws water from surrounding tissues toward the gut to dilute the drink before it can be absorbed. This process can deepen dehydration rather than correct it, particularly with very sweet drinks consumed in large quantities.

The caffeine in soft drinks, coffee and tea has a mildly diuretic effect at high doses, although the net effect at ordinary consumption levels is modest and does not fully cancel out the fluid content. The more important issue is that these drinks add significant calories and sugars without providing the same rehydrating effect per millilitre as water.

Water remains the best choice in all circumstances. If you find plain water unappealing, sliced cucumber, lemon, mint or orange in a jug of water improves the flavour without adding sugar. Mineral water adds natural minerals including sodium and magnesium that support hydration during and after physical exertion.

Hydration during Ramadan

Ramadan in summer presents a genuine physiological challenge, particularly in countries where fasting hours extend to 15 or more during extreme heat. A person who is physically active outdoors and fasting simultaneously faces the combined effect of heat, exertion and no fluid intake for many hours. This combination is a real medical risk rather than a theoretical concern.

The practical strategy for hydration during Ramadan: begin iftar with water before food, distribute your fluid intake gradually across the hours between iftar and suhoor rather than drinking large volumes at once on an empty stomach, and prioritise water-rich foods including vegetables, soups and fruits. Suhoor meals that are heavily salted increase thirst during the day and are worth moderating.

People who work outdoors during summer Ramadan should discuss their specific situation with a doctor before the month begins. Some health conditions make fasting in extreme heat a genuine medical risk that warrants medical intervention or religious dispensation from fasting, and this conversation is better had in advance.

Special hydration needs

Certain groups need closer attention to hydration than others. People with diabetes lose additional fluid when blood glucose is elevated because the kidneys work to excrete excess glucose through urine, drawing water with it. This is why uncontrolled diabetes is accompanied by significant thirst and frequent urination, and why keeping glucose controlled is also a hydration management issue.

People with a history of kidney stones benefit substantially from high fluid intake. Adequate hydration dilutes urine and reduces the concentration of minerals that form stones. Nephrologists across the region commonly recommend more than three litres daily for people with a stone history, tailored to the individual and the type of stone they form.

Pregnant and breastfeeding women need more fluid than the average adult. Breastfeeding requires an additional 700 to 800 ml of fluid daily above baseline needs. Dehydration in a breastfeeding mother living in a hot climate can affect milk supply and quality, which is a practical concern that traditional advice often underaddresses.

Foods that contribute to hydration

Water in food contributes 20 to 30% of total daily fluid intake for people who eat fresh produce. Cucumber is approximately 95% water by weight, tomatoes around 94%, and watermelon over 90%. These foods contribute meaningfully to your daily fluid total while also providing minerals and antioxidants that plain water cannot. Including water-rich vegetables and fruits in your daily meals is a practical hydration strategy, not just a nutritional one.

Soups and broths are also meaningful contributors to hydration and add natural sodium that supports fluid retention in the body. In Arab cooking, soup is a natural part of both iftar and dinner, which incidentally supports hydration throughout the day without requiring deliberate effort.

Foods that are heavily salted, including pickles, salted cheese, and heavily seasoned dishes, increase thirst and require additional water to restore sodium balance. This is not harmful in itself but means that a salt-heavy meal in summer should be followed by additional water, not less.

Building a reliable daily hydration habit

Counting glasses is tedious and most people stop within a few days. A more durable approach builds drinking into existing routines. Start each morning with a large glass of water before coffee or tea, because sleep itself causes mild dehydration over seven to nine hours without fluid. Keep a water bottle visible throughout the day, as visual presence is one of the most reliable triggers for drinking.

Drink a glass of water before each main meal. This contributes to your daily total and sometimes reduces the amount you eat at that meal because the stomach is partially occupied. In hot weather, add a glass or two after any outdoor exposure or physical activity beyond light walking.

Do not rely on thirst as your primary signal in very hot and dry climates like the Syrian, Iraqi or Gulf desert environments. Sweat evaporates so quickly in dry heat that you may lose significant fluid without noticing it on your skin. A timed drinking schedule is more reliable than waiting for thirst in these conditions, and checking your urine colour twice a day gives you an honest feedback loop.

Sources

• Albasheer OB et al. Awareness of dehydration state and fluid intake practice among adults in Jazan Region, Saudi Arabia. Journal of Nutritional Science, 2021.
• Al-Bouwarthan M et al. A Field Evaluation of Construction Workers Activity, Hydration Status, and Heat Strain in the Extreme Summer Heat of Saudi Arabia. Annals of Work Exposures and Health, 2020.
• Bates GP et al. Hydration status of expatriate manual workers during summer in the Middle East. Annals of Occupational Hygiene, 2010.
• Kavouras SA. Assessing hydration status. Current Opinion in Clinical Nutrition and Metabolic Care, 2002.
• Armstrong LE et al. Urinary indices of hydration status. International Journal of Sport Nutrition, 1994.
• World Health Organization: Water, Sanitation and Health