This is a very tough question to answer, and there are many ideas on this. The recent evidence suggests that we need 33 milliliters for each kilogram of body weight. For a 70kg person, that would equate to approximately 2.3 litres per day. The important thing to remember for this is that this doesn’t have to be just drinking water as lots of our food has a high water content. This is a suggested total fluid intake. Up to 20% of our water intake can come from food. The old adage of '8 glasses per day' can get you close but may be quite far off for a bigger person.
This is the current suggested amount but it is not set in stone. Varying things may mean you need more than this. These include:
- Exercise. Vigorous exercise mean you will lose more water than normal, hence you will need to increase your intake.
- Environment. If you are in a hot or humid environment you will need more water as you tend to sweat more.
- Illnesses. Some illnesses like vomiting or diarrhea will mean you lose more fluid hence you will need to replace this.
- Pregnancy or breast feeding. These can often require more fluid.
- Diuretics. Drinks like coffee and alcohol are diuretics (make you go to the toilet more) hence cause you to loose water. If you are having a lot of these you will need to increase your intake.
The link between water and pain
A 2016 study published in Psychophysiology, examined the experience of pain as it relates to hydration. They found that those who had hypo-hydration (not enough water but not dehydrated) had higher sensitivity to pain. Simply, not being well hydrated, can apparently intensify the experience of pain. The researchers said that more studies were needed to evaluate the mechanism of this effect, but it is a great starting point.
Pain is a complex thing and I will do a post purely on this soon. If you are in pain, making sure you are well hydrated is a simple thing you can do that may make you feel better. As a bonus, if you are drinking more water the rest of your body will function better too. Of course you will need to find out what is causing the pain, but if simply increasing your water intake will help you manage the pain better, your body will thank you for it.