With the warm months in front of us this question from a reader carries some important implications.
Can I ask (might be obvious) how much water is enough? I know I can drink too little (although I don’t… about 2.5-3 liters) but can I drink too much? I know that if I drink before a run I will be crippled with cramps and it might depend on body mass or just the person but in the scale of the day can one person drink too much water?
For your immediate answer look to the end of this post. But it is far better to understand the big picture before answering your question. Let’s start with fluids to sustain a healthy life. According to the Insitute of Medicine an adult male should consume the equivalent of 13 eight ounce glasses fluid* and an adult woman should take in 9 eight ounce glasses. That is about 3 liters and 2 liters respectively. Other sources state the commonly quoted 8 eight ounce glasses per day. Approximately 20% of your fluids are from food in a typical diet.
(*Note I did not say “water” purposely.)
Next, you need to to calculate how much water is sweated out during exercise. This is highly individual so do this test. There is no formula that works for everyone.
1. Weigh yourself naked.
2. Go, run a specific time (instead of distance) at a common effort or pace. (Oh, get dressed first.)
3. Upon return – and without drinking any fluids – weigh yourself once again naked.
You now know how much weight you lose in 30 minutes or 60 minutes or whatever. You can extrapolate water loss for all other runs this way.
Each pound of weight lost is about a pint of fluid (US; or about 1.25 pounds for the imperial pint). That becomes the amount – over and above – the healthy life sustaining fluids mentioned above that you must add to your daily intake.
Variables to consider:
Size matters. The larger the person, the more the fluid will be needed.
Heat matters. The hotter the temperatures the higher the body temperatures and therefore increased sweating to help dissipate body heat.
Health status matters. Vomiting, fevers and diarrhea adversely effect body fluid levels.
Altitude matters. You lose more fluids above 2500m/8200ft. in elevation.
Humidity matters – kinda. Sweat does not cool. Evaporation of sweat cools. Humid conditions decrease evaporation and therefore decreases the cooling effect. This may stimulate even more sweating as body temperatures rise (due to lack of cooling). But, for the most part, you sweat equally as much in dry climates as humid ones. It’s just that in the dry climates it evaporates from the skin fast so you don’t see it.
This from a Proctor & Gamble study that awarded Phoenix the “Sweatiest City” title: The average Phoenix resident produced 26 ounces (0.77 litre) of sweat per hour during a typical summer day last year when the desert city’s high temperature averaged 93.3 F (34 C). (Note – non-exercising.) Jay Gooch, sweat expert at Old Spice, a Procter & Gamble Co. antiperspirant brand stated, “Phoenix’s humidity was only 22 percent, making it much more comfortable than Miami, with average temperatures last year of 83.9 F (29 C) and humidity of 76 percent, according to government figures. In Phoenix you sweat much more than in Miami, but it evaporates quickly as it is such dry air so you don’t notice as much. In Miami the sweat stays on your skin.”
Now to answer the question of too much water. The answer of course is yes. An extremely high volume of water dilutes your body’s electrolytes. In the case of VERY long endurance runs hyponatremia is one possible condition. Without getting into this topic too much – it usually happens to joggers/walkers who are out for many hours all the while drinking plain water by the gallons. They simply over-hydrate. This is rare and uncommon amongst well trained individuals despite the media attention to this very serious but statistically rare condition.
Acutely, if you drink too much too close in time to your run you can also most definitely be guilty of over-drinking. Though it won’t effect electrolytes it may predispose you to stomach cramping or puking. The rule of thumb is to drink about a liter (16 ounces) 1-2 hours before running. During workouts, if your stomach sloshes from fluid intake – you drank too much.