The days are growing longer, and the weather is becoming progressively warmer.  With the winter hibernation coming to a close for another year, many people are crawling out of their indoor caves, and spending more time outside.  There is an undeniable association between the warmth of the sun and our desire to be active.  We all know however, that when we increase our physical activity, especially as the temperature rises, our bodily demands for fluids also increase.  But are we doing enough to prevent dehydration that is inevitable from inadequate fluid intake?  If you are getting thirsty, the answer is no!

Importance of Water

Water is the largest component of the body, making up 60% of total body mass in the average lean adult.  It is found within and between every single cell.  Our blood, cerebrospinal fluid, synovial fluid, and lymph are primarily made of it.  It powers digestion, lubricates our joints, permits respiration, is vital in oxygen delivery to our tissues, and removes toxins from the body.  Needless to say, water is a requirement for life, and is grossly taken for granted!

Understanding Thirst and Dehydration

The thirst sensation is not a warning for pending dehydration, as commonly believed.  In reality, it is triggered by actual dehydration—so if you are feeling thirsty, you are already dehydrated!  The ‘Thirst Center’ is an area of the brain located in the hypothalamus, specifically the periventricular nuclei (for those who like to get technical).  It is responsible for gathering information from the body, and alerting us when there is insufficient water in the system.  There are three main ways that the brain detects dehydration from receptors in the body:

  1. Dry mouth and pharynx from inadequate water to produce saliva.
  2. Increased osmolarity (concentration) of the blood.  Essentially, water dilutes blood to the proper concentration, and when water is lacking, blood becomes more concentrated than it should be.
  3. Decreased blood pressure from a decreased blood volume, since blood is largely made of water.
Daily Water Requirements

The human body lacks a long-term water storage system.  Water is lost primarily through the urine, but also in the feces, lungs, and skin. Needless to say, any water lost must be replaced in order to maintain health.  But how much is necessary?  This is a far more complicated question than likely perceived.  Water demands change depending on body size, composition, medications, ingested diuretics (caffeine/alcohol), physical activity, gender, and age.  Most people are familiar with the 8 glasses/day recommendation, but it takes for granted the individuality of people.

Sparing the complicated rational for why, a more accurate calculation for adults is:

Water Intake = 35 [ml/kg] x current weight [kg]

Simply plug your current weight (kilograms) in to the equation, to find out how many millilitres of water you should be consuming per day.  Please note, this is the total water needed for healthy function, and some water is gotten through ingested food, so the number will be slightly higher than the amount of pure water that should be drank.  Also note, this does not hold true for children and infants, and is insufficient in hot climates, and with strenuous exercise.

Water should be consumed spread throughout the day.  While pop and juices are primarily made of water, they dehydrate the body and are not acceptable replacements for pure water.

Water Demands Change with Increased Physical Activity

The above guidelines are only to maintain healthy hydration on a daily basis, at a mild level of activity.  If you are an athlete, or are participating in a strenuous activity, a water intake above and beyond is necessary, and this requires more planning.  To avoid dehydration follow these guidelines:

  • Consume 500 ml of water one hour prior to your activity to maximally hydrate your tissues.
  • Water should be consumed at a rate of 500 ml/hour during moderate activity and 750-1000 ml/hour during strenuous activity.
  • Rehydration following activity is just as important as hydration during activity.  Weigh yourself before and after exercise to find out how much water weight you lost.  Drink 600 ml for every pound lost!
  • If you have salt residue on your clothing, you are losing electrolytes that should be replaced. Consider a 6% electrolyte beverage during activity to maintain electrolyte levels.
Can You Drink too much Water?

As with anything, it is possible to get too much of a good thing.  Water intoxication is a real medical problem, though exceedingly rare.  Healthy individuals would need to vastly over consume water in order to be affected.  There is ample medical evidence showing that it is far safer to slightly exceed daily water requirements then to be chronically under-hydrated.  Though, it is always best to feed your body the same amount of water that it requires for optimal function.  If you have a pre-existing medical condition, especially kidney or heart disease, always seek professional guidance before making large changes to your fluid intake.