How much water should you drink in a day? The ballpark figure recommended by authorities is 8 glasses per day or 2 litres on average. Needs vary depending on your body composition, time of year, stage of life, overall health. All these influence how much water does your body needs for optimal health. We look at these needs in depth.
Body water: the basics
We are all water!
On average the body is 45-75 per cent water. The composition varies based on your body composition, age, gender amongst others. For example, babies are about 75% water whereas older people could be around 50%. Men tend to have more water than women because their bodies contain on average more lean muscle which contains more water than lipids. If you are leaner, you will have a higher % of water, as lean muscle contains about 73% water whereas body fat is only about 25% water.
What does water do?
Water is the nutrient we need by far the most – it surrounds our cells and every bodily function takes place in a watery medium. H2O regulates body temperature. It also dissolves nutrients and transports them along with oxygen and carries waste products away. Water moistens body tissues and is the main part of every body fluid, including food, gastric acid, saliva, amniotic fluid (baby development) and urine. It helps to lubricate joints and cushion organs and tissues.
Water also is a source of many essential minerals we need to function properly and achieve optimal health.
How much water should you drink in a day?
How much water should you drink in a day depends on how much you lose daily. We need to drink enough water to maintain a water balance and replenish any liquids lost. The average adult loses about 2.5 quarts (2.5litres) of water daily. This is lost via perspiration , toilet visits and even breathing. During hot days or strenuous workouts the loss will be greater.
The body does not store water like other nutrients…
The Institute of Medicine in the USA recommends total intake of 3.7 litres for men and 2.8 litres for women on average. This would include any water from food and other sources which counts towards the total.
What are the things that influence our water requirements?
- Extreme temperatures – hot or cold – the body uses more water to maintain its normal temperature
- High altitudes (8.2k ft or 2.5k metres) may increase urine output and raise the heart rate => increased water loss
- Strenuous work or exercise – drink more before and during
- Heated or circulated air (in airplanes or air conditioned environments) causes more water loss and skin dryness
- Pregnancy and breastfeeding increases water requirements. For pregnant women these go up to 3 litres a day and for breastfeeding women 3.8 litres/ day
- Fever diarrhea and vomiting also cause water loss and increased requirements
- High fibre diets, also require higher water intake as much water is absorbed by fibre in the body
What happens when you are dehydrated?
Because drinking enough water is all about balance, that depends on the percentage of body weight that is water loss. The more body weight is lost to dehydration the more severe the effects…
0-1% => thirst
2-5% => dry mouth, flushed skin, fatigue, headache, impaired physical performance
6% => increased body temperature, raised breathing rate and pulse
8% => dizziness, increased weakness, labored breathing with exercise
10% => muscle spasms, swollen tongue, delirium, wakefulness
11% => poor blood circulation, failing kidney function
Can you drink too much water?
The kidney can eliminate excess water, up to 24 ounces/ hour, so you probably won’t overdo it…
Here are some of the small practical steps to ensure you drink enough water.
- Drink mostly water and fluids without sugar or calories
- Take water breaks during the day – try and replace at least 1 snack with a glass of water instead J
- Drink water with food – this will keep you fuller
- Drink water before, during and after any physical activity
- Keep a bottle of water with you at all times when travelling
Tap of bottled water?
Both tap and bottled water are regulated. Especially in large municipal water systems tap water is fine to drink. Tap may also contain safe levels of fluoride a mineral which helps harden developing tooth enamel and so protects tooth from decay.