Beginners hydration questions

Hi Folks,

I am currently doing the C25K and have slightly modified the values in order that I will be running 40 mins at the end of the 9 weeks ( rather than the given 30).

My question is as follows.  At what point will it be necessary to start taking water for hydration.

I understand that several factors are import, so I will list that points that I believe influence the decision.   Please feel free to correct, amend or offer any points of view that will improve my understanding.


1 : At the moment it is approx 0°C ( 32°F) so I presume that the cold weather will remove a lot of the requirement to drink.  I imagine that the quantity of required fluid will also rise exponentially with the increase in heat.  But even in the cold do any of you take water ?

2 : Increased heart rate percentages will also influence body heat and increase sweat + fluid loss.  Is there any way to anticipate how much fluid should be consumed, pre-session / during session in relation to the zones that are intended for the run.

3 : Time of day - Is there any difference between running in the morning compared to later in the day.  I usually run at 06:00 am and quite honestly don't feel like drinking before I go out, at most maybe a small glass.  I usually drink half a litre when I return.

4 : Duration : I am only out for 30 minutes at a time for the moment, I don't currently take any water with me and I am slowly increasing the duration.   I usually run around 78% HR .  How could I approximate the duration at which I should start to take some water ?

If I have understood correctly it takes about 20 minutes for the body to absorb any fluid so any run under 20 minutes doesn't need any fluid intake.  I would imagine that any run under 40 probably wouldn't require anything other than a glass before the run.  After that, I really have no idea what would be the best approach.

I don't suffer from cramps or ever appear to have signs of dehydration.  Due to my short running times I doubt that it will be a problem for the moment but I am planning in a fun run 7.5k in December which I presume will take me about an hour.

Thanks in advance for any and all advice that you can offer and please feel free to correct me for anything that I have not quite understood.

Cheers Roy




  • Don't overthink this or take a lot of advice. It's your body.

    I'm happy running for 2 hours/13 miles without water some days. Other days I'm sipping from my bottle 1 mile into a 6 miler.

    If you are hydrating properly during the week you probably won't need any water on runs under 40-60 mins.

    Don't drink too much, it's far more dangerous than drinking too little.
  • You really don't need to take any water with you. Your body copes brilliantly being slightly dehydrated.

    I know I used to drink more when I began running but I think it was more of a comfort thing than a real need.

    By all means take water if you want to - but you'll be fine if you don't.

    Now I can run for a good few hours without fluid if it's not hot.
  • listen to your body but anything under 1 hrs running in this weather you should be fine without.
  • If i'm going for 10km or further I take liquid with me.  If i'm doing less i don't bother, but that's just me.  I'm sure everyone is different.


  • Wow, I am surprised to learn that I don't really need to bother for the moment. ( Which is a good thing as carrying a bottle of water in 0°C doesnt really excite me , lol).

    Thanks for you replies guys.

  • There's been a lot of money spent convincing you that sports drinks are vital. Always by the manufacturers. Strange eh ?
  • Hi UC,

     Are those "After the Run" recuperation drinks in the same league..   My local running shop wants to convince me that they are very important.

  • After a run have a glass of milk.

  • Roy, are you by any chance some kind of scientist? Just asking because you seem to think there might be a precise formula which will tell you exactly how many millilitres of water you should drink at exactly x minutes into your run, and it really doesn't work like that. TimR is right, it's actually fairly simple.

    You should be fine with no water on runs of up to an hour in all but the hottest weather. However if you feel thirsty on short runs and want to take water with you, fine. As your body adapts to running, you'll be able to run further without feeling like you want a drink. Some people drink more than others while running; some people sweat more. If you like calculations (I suspect you do image ) and you want to figure out correct hydration for longer runs, you can weigh yourself before and after runs to see how much weight/fluid you've lost through sweating, which would help you get a rough idea of how much fluid you lose in an average hour of running, and therefore how much water you should take with you for longer runs to prevent dehydration. Of course it'll only ever be a rough guide, as your rate of sweating will vary depending on weather, route, intensity etc.

    On a very hot day this summer I weighed myself before and after a hilly 10 mile run and found I had lost 2.5lbs. But I had also drunk 650 mls of water while running so had actually sweated off almost 4lbs!

    P.S. One flaw in your reasoning: "1. The cold weather will remove a lot of the requirement to drink." A totally reasonable assumption, but not entirely correct. When you inhale, you humidify air and heat it up to your body's temperature before you exhale it. In cold weather or at high altitudes the air you breathe is drier. So your body has to work harder to humidify it. So although you may not be sweating as much when it's very cold, you're losing more moisture than you normally would just through breathing. Plus because you're not getting hot you tend to feel less thirsty, meaning it's actually much easier than you think to become dehydrated in cold weather.

    Just realised that I started by saying 'it's actually fairly simple' then have gone on to waffle at length and over-complicate things. LOL!

  • Lol. That's a good point about cold dry weather. I do a lot of walking in the hills in winter. I used to forget to drink. The first acute sign of dehydration is a stinking headache. That's why you get a headache with a hangover. If you find you are suffering with headaches in the few hours after running, then you should probably drink more.

    I've found performance does suffer if I become dehydrated. Bearing in mind o think the human body has something like 70% water. That's 0.7 litre for every kg. For a 70kg man a 2% loss equates to a litre of water. You'll feel pretty thirsty at that point. Headaches and other symptoms occur at around 5%.

    Learn to listen to your body. A skill modern life and sports articles seem to have robbed from a lot of us.
  • I always drink a small cup of water before leaving regardless of distance. If the run is

  • Steve. Did you use the "less than" symbol. That would explain why the rest of your post is missing.
  • Dear Dog,

    Thank you for your response, and yes I laughed at its simplicity..  Am I a scientist, no, but I suppose that 20 years of IT kinda makes me a little bit geek.

    Your reply concerning the cold weather is definitely interesting in relation to the effort required to transform the humidity.

    The main reason that I ask for such detail is simply down to the fact that as a 46 year old ex-smoking beginner I want to try and avoid injury which might be caused by my ignorance.  I run alone and I get any advice from anyone I know, no-one is a runner.

    The geek side of me can't help but look towards the technical side of things for answers, although I do realise that simply listening to ones body is sometimes all that is required.  But then again if you arrive at feeling signs of dehydration it usually means that you are already too late image.

    Anyway thanks for the information, I probably have a long way to go yet before requiring to carry some water....  I learn slowly but I learn...

    Cheers Roy


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