Following on from my recent water-related comments, I felt it was important, given recent media attention, to clarifying the safety of water drinking and simple rules to follow to ensure you are doing it safely.
This was brought about by recent scares from media reports sparked by a lady who died in a contest because of over-consumption of water. Many people are now concerned about their water drinking and are tending to drink less for fear of this happening to them.
So...how much is too much?
About 70% of the fat free mass of the human body is made of water. To function properly, the body requires between one and seven litres of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. Although it differs per individual most experts agree that 8-10 large glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration. Where it is possible I tend to advice 2-4 liters per day for a normally active healthy adult.
Dehydration is the cause of most general malaise and feelings of energy loss, lethargy, poor skin quality and general immune system level decreases. Whilst it is actually difficult to drink too much water, it is certainly physically possible for people to drink far more water than necessary, putting them at risk of water intoxication, and yes, this can be fatal.
Water intoxication results from the over-dilution of sodium in the body (hyponatremia). Water intoxication is most commonly seen in infants under six months of age and sometimes in athletes, but can occur in anyone if they drink too much water all at once. It occurs when a dehydrated person drinks too much water without the accompanying electrolytes, or drink too much water at once, over-diluting electrolytes in the body.
When too much water enters the body's cells, the tissues swell with the excess fluid. Your cells maintain a specific concentration gradient, so excess water outside the cells (the serum) draws sodium from within the cells out into the serum in an attempt to re-establish the necessary concentration. As more water accumulates, the serum sodium concentration drops (hyponatremia).
The other way cells try to regain the electrolyte balance is for water outside the cells to rush into the cells via osmosis. The movement of water across a semipermeable membrane from higher to lower concentration is called osmosis. Although electrolytes are more concentrated inside the cells than outside, the water outside the cells is 'more concentrated' or 'less dilute' since it contains fewer electrolytes. Both electrolytes and water move across the cell membrane in an effort to balance concentration. Theoretically, cells could swell to the point of bursting.
From the cell's point of view, water intoxication produces the same effects as would result from drowning in fresh water. Electrolyte imbalance and tissue swelling can cause an irregular heartbeat, allow fluid to enter the lungs, and may cause fluttering eyelids. Swelling puts pressure on the brain and nerves (hence the term “water on the brain”), which can cause behaviors resembling alcohol intoxication. Swelling of brain tissues can cause seizures, coma and ultimately death unless water intake is restricted and a hypertonic saline (salt) solution is administered. If treatment is given before tissue swelling causes too much cellular damage, then a complete recovery can be expected within a few days.
So how do we get the right balance?
The amount of water you need varies from person to person. You lose water every day through breathing, sweating, urinating, etc, and in order to balance this, you must replenish your supply by drinking water or other drinks and food containing water. The average adult urinates the equivalent of about 1.5 litres a day. So as a general rule if you aim for at the very least 2 litres a day, you should be covering whatever you have lost from sweating, breathing etc.
It's not how much you drink, it's how fast you drink it!
The kidneys of a healthy adult can process fifteen liters of water a day! You are unlikely to suffer from water intoxication therefore, as long as you drink over time as opposed to taking in an enormous volume at any one time. This is the simple key.
The media story consisted of a woman who was taking part in a timed competition to see who could drink the most water in a given time frame, on live radio! Ridiculous in terms of entertainment, and ultimately fatal. However, unless you are going to do something relatively stupid like trying to gulp down gallons of water at once, the bottom line is that it is possible to drink too much water, but unlikely under normal conditions.
Remember that it is much more dangerous (especially in warm humid weather and while exercising) to drink too little. You may need more water if the weather is very warm or very dry, if you are exercising, or if you are taking certain medications.
People suffer from dehydration every day, but rarely suffer from water intoxication except for in extreme circumstances. So keep to the simple rule of drinking your water throughout the day, not all at once, and drinking more if you are more active or hot on a particular day, and you will have no worries, and stay healthy!