The human body possesses remarkable resilience, capable of surviving for weeks without food. However, this endurance dramatically shortens when it comes to water, with survival lasting only a matter of days without it. This stark contrast underscores the indispensable role water plays in sustaining life.

Water constitutes a significant portion of our physical being, ranging from 50 to 75% of body mass. It is the foundational element of vital bodily fluids such as blood, digestive juices, urine, and perspiration. Furthermore, water is integral to the composition of lean muscle, fat, and even bones.

Unlike some nutrients, our bodies lack a mechanism to store water effectively. Consequently, we are reliant on a daily replenishment of fresh water to compensate for the continuous losses that occur through natural processes like breathing, perspiration, urination, and bowel movements. The precise amount of water needed daily is not a fixed figure; it fluctuates based on individual factors including body size, metabolic rate, environmental temperature, dietary habits, and levels of physical activity.

The Vital Roles of Water in Your Body

Water is not merely a component of our bodies; it is an active participant in countless physiological processes. Understanding the scope of water’s involvement highlights why we need water to thrive. Consider these crucial functions:

Cellular Health and Integrity: Water is essential for maintaining the health of every single cell in your body. It acts as a solvent, facilitating chemical reactions within cells and contributing to their structural integrity.
Liquid Bloodstream: Water ensures that our blood maintains the necessary fluidity to navigate the intricate network of blood vessels. This is critical for efficient transport of oxygen and nutrients throughout the body.
Waste Elimination: Water plays a pivotal role in flushing out metabolic by-products, excess electrolytes like sodium and potassium, and urea – a nitrogenous waste product from protein metabolism. These substances are dissolved in water and expelled primarily through urine.
Body Temperature Regulation: Through sweating, water is instrumental in regulating our internal temperature. Evaporation of sweat from the skin’s surface has a cooling effect, preventing overheating, particularly during physical activity or in warm environments.
Moisturizing Mucous Membranes: Water keeps mucous membranes, such as those lining the lungs and mouth, adequately moist. This moisture is vital for their protective function and overall comfort.
Joint Lubrication and Cushioning: Water acts as a lubricant and shock absorber for our joints. Synovial fluid, which is largely water-based, ensures smooth joint movement and cushions bones during impact.
Urinary Tract Health: Adequate water intake is crucial for preventing urinary tract infections (UTIs). By maintaining a steady flow of urine, water helps to keep the bladder and urinary tract clear of bacteria, reducing the risk of infections like cystitis.
Digestion and Constipation Prevention: Water aids in the digestive process, helping to break down food and move it smoothly through the digestive tract. It also softens stools, preventing constipation and promoting regular bowel movements.
Skin Health and Appearance: Water moisturizes the skin from the inside out, contributing to its texture, elasticity, and overall healthy appearance. Dehydration can lead to dry, flaky skin.
Nutrient and Oxygen Transport: Water is the medium through which nutrients and oxygen are carried to cells throughout the body. It ensures efficient delivery of these essential elements for cellular function and energy production.
Shock Absorption: Water acts as a protective cushion within critical areas, including the eyes, spinal cord, and the amniotic sac that surrounds a fetus during pregnancy, safeguarding these delicate structures from physical shock and injury.

Getting Water from Food and Fluids

While we instinctively think of drinking water to meet our hydration needs, it’s important to recognize that our bodies also obtain water from food. In fact, a surprising amount of water is present in many foods, even those that appear dry. On average, approximately 20% of our daily water requirement comes from solid foods.

Furthermore, the very process of digesting food generates a small amount of water as a byproduct. This metabolic water can contribute to about 10% of the body’s total water needs.

This leaves roughly 70% of our water requirement to be fulfilled through direct fluid intake. This underscores the necessity of consciously consuming beverages throughout the day to maintain optimal hydration.

How Much Water Should You Drink Daily?

The question of “how much water should I drink?” is a common one, but the answer isn’t a one-size-fits-all recommendation. The Australian dietary guidelines advocate for drinking “plenty of water,” acknowledging that individual needs vary considerably.

The daily fluid requirement is influenced by a range of factors:

Gender: Generally, men tend to have slightly higher fluid needs than women due to differences in body composition and metabolism.
Age: Fluid requirements change across different life stages, with infants, children, and the elderly having specific considerations.
Activity Level: Individuals who are more physically active, whether through exercise or demanding occupations, require more fluids to replace those lost through sweat.
Pregnancy and Breastfeeding: Pregnant and breastfeeding women have increased fluid needs to support both their own bodies and the developing baby or milk production.
Climate and Weather: Hot and humid weather conditions lead to increased sweating and thus higher fluid requirements.
Lifestyle: Dietary habits, such as consumption of high-water content foods, and overall health status can also play a role.

The table below provides general guidelines for adequate daily fluid intake across different age groups and conditions. It’s important to note that these are adequate intakes, encompassing all sources of fluids, but prioritizing plain water as the primary beverage is generally recommended, except for infants who primarily obtain fluids from breast milk or formula.

Infants 0–6 months*	0.7 liters
Infants 7–12 months#	0.8 liters total (with 0.6 liters as fluids)
Girls and boys 1–3 years	1 liter (about 4 cups)
Girls and boys 4–8 years	1.2 liters (about 5 cups)
Boys 9–13 years	1.6 liters (about 6 cups)
Boys 14–18 years	1.9 liters (about 7–8 cups)
Girls 9–13 years	1.4 liters (about 5–6 cups)
Girls 14–18 years	1.6 liters (about 6 cups)
Men 19 years+	2.6 liters (about 10 cups)
Women 19 years+	2.1 liters (about 8 cups)
Pregnant girls 14–18 years	1.8 liters (about 7 cups)
Pregnant women 19 years+	2.3 liters (about 9 cups)
Lactating girls 14–18 years	2.3 liters (about 9 cups)
Lactating women 19 years+	2.6 liters (about 10 cups)

from breastmilk or formula

from breastmilk, formula, food, plain water and other beverages*

It’s also worth noting that certain individuals may require less fluid than these general recommendations. This includes those who consume a significant amount of water-rich foods like fruits and vegetables, live in colder climates, or lead largely sedentary lifestyles.

Conversely, some people have increased fluid needs. These include individuals:

Following a high-protein diet, as extra water is needed to assist the kidneys in processing protein.
Consuming a high-fiber diet, where water helps prevent constipation associated with increased fiber intake.
Experiencing vomiting or diarrhea, where fluid losses must be replaced to prevent dehydration.
Engaging in physical activity, to replenish fluids lost through sweat.
Exposed to warm or hot conditions, also to compensate for sweat losses.

Athletes, in particular, have complex hydration needs influenced by exercise intensity, duration, and environmental conditions. Fluid requirements for athletes are highly individualized and should be tailored to their specific circumstances.

Tips to Increase Your Fluid Intake

If the idea of drinking numerous glasses of plain water feels unappealing, remember that “fluids” encompass a wide variety of beverages beyond just water. These include milk, coffee, tea, soup, and juice.

While all fluids contribute to hydration, plain water is often considered the optimal choice. It is calorie-free and highly effective at hydrating the body. Tap water is also readily accessible and usually cost-effective.

However, other beverages can also offer benefits. Milk, for instance, is approximately 90% water and provides essential nutrients, particularly for children. Tea can contribute to daily fluid intake and offers antioxidants and polyphenols, which may have protective effects against heart disease and cancer.

If you prefer fruit as a fluid source, prioritize whole fresh fruit over fruit juice. Whole fruits provide natural juices along with beneficial fiber and nutrients, while limiting the intake of added sugars often found in fruit juices.

Here are some practical tips to help you drink more water throughout the day:

Flavor it up: Add slices of lemon, lime, cucumber, strawberries, or mint leaves to plain water to enhance its taste and appeal.
Keep it handy: Always keep a water bottle or glass readily available on your desk, in your bag, or in your car as a visual reminder to drink.
Drink with meals and snacks: Make it a habit to drink water before, during, and after each meal and snack.
Fruity ice: Freeze fresh fruit pieces in ice cube trays and add them to your water for a refreshing and flavorful twist.

Dehydration: Risks and Symptoms

Dehydration occurs when the body loses more fluid than it takes in, leading to a deficiency in its water content. Fortunately, mild dehydration is usually easily remedied by simply increasing fluid intake. However, understanding the symptoms and causes of dehydration is crucial for timely intervention.

Symptoms of dehydration can range from mild to severe and may include:

Thirst
Headache
Lethargy and fatigue
Mood changes and slowed reaction time
Dry nasal passages
Dry or cracked lips
Dark-colored urine (a key indicator)
Muscle weakness
Tiredness
In severe cases: confusion and hallucinations

If dehydration is left unaddressed, it can progress to a critical stage where urination ceases, kidney function fails, and the body’s ability to eliminate toxic waste products is compromised. In extreme instances, dehydration can be life-threatening.

Several factors can contribute to dehydration:

Insufficient water intake
Increased sweating due to hot weather, humidity, strenuous exercise, or fever
Reduced thirst sensation, particularly common in older adults
Increased urine output due to certain hormonal imbalances, diabetes, kidney disease, or diuretic medications
Diarrhea or vomiting, leading to significant fluid loss
Recovery from burns, where fluid loss is a major concern.

Certain populations are at a higher risk of dehydration:

Babies and children: Their smaller body size and higher metabolic rate make them more vulnerable, especially during illness.
Elderly individuals: Age-related changes in kidney function, thirst mechanisms, and medication use can increase dehydration risk.

Babies and children are particularly susceptible to dehydration, especially when they are ill with vomiting, fever, or diarrhea. Dehydration in infants and young children can rapidly become a serious medical emergency. Seek immediate medical attention at the nearest hospital emergency department if you suspect dehydration in a baby or child.

Signs of dehydration in babies and children can include:

Cold skin
Lethargy and decreased activity
Dry mouth
Bluish skin tinge (due to slowed circulation)
Sunken fontanelle in babies (the soft spot on the top of the skull).

Elderly individuals are also at increased risk due to a combination of factors:

Age-related decline in kidney function
Hormonal changes
Diminished thirst sensation
Use of medications like diuretics and laxatives
Presence of chronic illnesses
Heat stress susceptibility
Limited mobility, which can hinder access to fluids.

Water Intoxication (Hyponatremia)

While dehydration is a common concern, it’s also possible, though less frequent, to overhydrate and experience water intoxication, also known as hyponatremia. This condition arises when drinking excessive amounts of water dilutes the sodium concentration in the blood to dangerously low levels.

Sodium is a crucial electrolyte that plays a vital role in muscle contraction, nerve impulse transmission, and maintaining fluid balance. When excessive plain water is consumed rapidly, the kidneys may not be able to eliminate the fluid quickly enough, leading to blood dilution and sodium depletion.

Hyponatremia can manifest with various symptoms, including:

Headache
Blurred vision
Muscle cramps, potentially progressing to convulsions
Brain swelling
In severe cases: coma and even death

It’s important to emphasize that water intoxication is rare in the general population. It typically occurs when exceptionally large quantities of water are consumed within a short timeframe.

Hyponatremia is more commonly observed in individuals with certain medical conditions or mental illnesses, endurance athletes who overdrink during prolonged events, and infants who are fed overly diluted infant formula.

Fluid Retention and Water Intake

A common misconception is that drinking water contributes to fluid retention (edema). In reality, the opposite is often true. Adequate water intake can actually help the body eliminate excess sodium, which is a primary factor in fluid retention.

The body tends to retain fluid when it perceives a lack of water within cells as a survival mechanism. When the body receives a consistent and sufficient supply of water, it no longer needs to hoard fluid, leading to a reduction in fluid retention. Therefore, drinking enough water can be a natural strategy to manage and reduce fluid retention.

Where to Get Help

For any health concerns related to hydration or dehydration, or in case of a medical emergency, seek professional help:

In an emergency, always call emergency services.
Visit the emergency department of your nearest hospital.
Consult your General Practitioner (GP) or family doctor.
For dietary advice and guidance, reach out to Dietitians Australia.
Seek nutritional information from Nutrition Australia.
Refer to the Australian Guide to Healthy Eating for general dietary recommendations.

Staying adequately hydrated is fundamental to overall health and well-being. Understanding why we need water and adopting healthy hydration habits are essential steps towards a healthier life.

Why Do We Need Water? The Essential Reasons for Hydration