Hydration in Sports: How much water to drink?

The calculator works by collecting, in which your body data (age, weight, gender) and your current hydration status. This means that we are asking: Are you starting your activity with a fluid deficit or are you well hydrated? The hydration calculator then asks for information about which activity you will be doing and how strenuous it will be. The intensity of the exercise has a more significant influence on your fluid requirements than any other factor. Do you run for 30 minutes at your personal limit? Or is your 30 minute run at more of a comfortable jogging tempo? Your sweat production and therefore your hydration requirements can be very different. Lastly, the calculator asks for information about the prevailing environmental conditions when you are doing your activity. Running in 35° is very demanding for the body and requires more cooling than in temperatures of 27°. The environmental conditions have a large influence on how much you sweat.

The calculator takes all of these entries and evaluates them and gives you two guidelines:

1. The amount of water your need during the activity, in order to replace the lost fluid.
2. How much water you should drink per hour

The second recommendation assumes a steady level of hydration throughout the activity – the goal is not to consume a large amount of water all at once at the end. Regular drinking makes it easier for the body to absorb the liquid and results in better functioning during activity.

The daily water requirements of the human body

How much water should you drink a day?

Our daily fluid balance is around 2.5 litres per day. If you start with around 300ml oxidation water, which comes from metabolic processes in the body (catabolism of glucose and fat for energy requirements) and we also consume around 700 ml fluid from solid food like fruits and vegetables, then we still need to drink around 1.5 litres of water, in order to achieve a balanced fluid intake.

Can you drink too much? What happens then?

You often hear the advice that you can't drink too much. But that is not actually true. This is totally irrational, since an excessively high liquid intake has no demonstrable benefits for the human body. Excess fluid in the body will just be excreted by the kidneys. As a result the urine becomes more weakly concentrated, and excretion increases. We just "get rid of" all the excess water and this is actually a further stress for your body.

When we sweat we lose not just water, but also a large amount of vital minerals. In endurance sports, the fear of dehydration often leads people to drink too much. This can eventually lead to the result that the minerals available in the body become extremely depleted and the body becomes mineral deprived, because the minerals are being excreted. Subsequently the minerals in the body become imbalanced and the body responds to this with a paradoxical symptom: Thirst.

If you then drink even more water, it is important to realise that the mineral content in the cells will get increasingly low, because the cells take in more and more water. This can lead to headaches, nausea and disorientation. In the most severe cases this can lead to swelling of the brain and even problems with the heart muscles. This phenomenon, which is known as "water poisoning", can even lead to death.

Dehydration and fluid deficiency

First signs of dehydration

In the early stages, dehydration is often noticeable because of the obvious symptom: thirst. However, in some people this feeling of thirst is less strongly pronounced or even totally lacking, especially in older persons. Symptoms like physical weakness or headaches can also point to dehydration. Dehydration is also strongly connected with a disturbance in salt levels (electrolyte maintenance).

Symptoms of dehydration

The signs of dehydration can be vary significantly and are also dependent on whether the body has predominantly lost water, electrolytes (salts) or both at the same time.

The physical symptoms of dehydration are:

• dry and pale skin, dry mucous membranes
• general feeling of weakness
• dark coloured urine
• Nausea and headaches
• Muscle cramps
• Clouding of consciousness, dizziness, disorientation
• Under-eye circles

It is really important when you are touring to watch out for these symptoms in your partner, so that you can spot dehydration early.

When does dehydration become dangerous?

Dehydration becomes more obviously noticeable depending on the severity of the fluid loss in mild dehydration the fluid loss amounts to 3 to 5% of the total bodyweight. The symptoms are thirst, mild dryness of the skin and mucus membranes as well as a noticeably darker urine colour.

Moderate dehydration is a fluid loss of 6 to 8% of the total bodyweight. Symptoms include sunken eyes, dry skin and mucus membranes, racing heart rate and a significantly reduction in urination.

In severe dehydration the fluid loss amounts to 9 to 12% of the body weight. This can lead to problems including very low blood pressure (hypotension) and poor skin elasticity: Take two fingers a pinch a fold of skin on your stomach or the back of your hand and let it go again; if the fold doesn't smooth out again right away, but holds its shape for a few seconds, you may be dehydrated.

If the dehydration reaches a level of 12 to 15% your body can go into shock. This can lead to extremely weak circulation, disturbances of consciousness like lethargy, extreme dizziness and delirium and even eventually to coma.

If you have extreme symptoms it is recommended that you get medical attention as soon as possible or if necessary notify the mountain rescue. The faster the affected person gets help, the better the outcome.

Meeting your fluid requirements

How can I meet my fluid requirements?

Ideal thirst quenchers are water and weak herbal and fruit teas. Whether it is better to drink tap water or carbonated/still mineral is a matter of personal taste. Caffeine containing beverages like coffee and black tea should not be your sole source of hydration, but can make up a part of your fluid balance, since they only have a temporary diuretic effect, not a long-term one. If you like, you can drink a glass of water with your coffee (like in traditional coffee houses). Alcohol in "higher doses" can have the effect of temporary dehydration. But when moderately consumed, alcoholic beverages like beer can in principle also be included in your fluid balance. The fluid found in food like fruit and vegetables can also be included in your daily fluid intake.

What do isotonic drinks and sports foods provide?

During sweating the body loses not only water by also minerals (electrolytes) like sodium and potassium. Isotonic beverages - also known as electrolyte drinks - contain the same concentration of minerals as blood, and are therefore taken up more quickly by the body. So the electrolytes lost through sweat can be rebalanced by the electrolytes contained in these beverages.

The extend to which hobby athletes need special sports drinks and what uses they have, is controversial and is dependent on the sport type and training intensity. Leisure athletes primarily need to replace the electrolytes and water lost through sweat.

Sweetened electrolyte drinks have the disadvantage, that the sugar delays the water uptake by the body. These don't need to be special and expensive isotonic beverages. Apple juice mixed in a 1:3 ratio with sodium rich mineral water provides an ideal isotonic beverage for endurance sports.

How do I meet my fluid requirements when touring outdoor?

There are many options to help you make sure that you always get enough water. Water bottles come in various sizes, and among these you are sure to always find one that is suited to the bottle holder on your bike, or the side pockets of your backpack. Hydration bladders with matching tube give the option of being able to transport large quantities of water comfortably in your backpack and to be able to take a drink quickly and easily when needed.

When you on the go and need to fill up your water receptacles, it is recommended that you use running water like clear mountain streams or natural springs and to study the surrounding environment. If the water is situated directly above cows in a meadow it is probable that the water is polluted. In general the water above the forest- and tree line in the mountains (where you will very seldom still find grazing animals) is more often safe to drink.

Melt water from snow and ice as well as water from wells or rainwater should only be drunk when there are no other water sources available. Melt water contains fewer minerals and can also be polluted by dirt particles.

The use of tablets for water purification enables you to make use of the water in regions where animals graze and in areas where there is generally little water available. It is very important to inform yourself before the tour about the availability of water in the areas you will be travelling.