After the hottest London marathon of all time last Sunday, lots of warnings were given out about runners needing to pace themselves and not go for personal bests.

One of the key aspects of staying safe is hydration. This is something that is very hard to get right. Drink too little and you may get ill,  drink too much and the same may happen. So what is the right amount of water?

Well, how much you need to drink on a run, depends on how much you sweat. Most people sweat around 24-32 ounces an hour whilst exercising, so you should aim to replace a least 75% of that.

Of course this is an inexact science. We all sweat at different rates. I found that on the New York Marathon last year, I had a small water bottle and just kept taking constant sips from it during the race. At every water station I topped up with more water or Gatorade and just kept it going steadily. However, it was cold and rainy, so I would have drunk slightly more on a hotter day. Just listen to your body and work out how much you are sweating.

By the way, your urine should be pale yellow or straw coloured before you go on a long run, so practice checking this on your training runs. If you get hydration wrong, you can’t play catch up on the course.

If you have salt marks on your face and clothes during and after the runs, you have sweated too much, so try salt capsules. We took one of these once an hour in New York and it worked a treat.

So, to sum up. There is no right answer, but practice your water intake in training. Try salt tablets and make sure you mix your water with an isotonic drink for electrolytes.

Happy safe running!