Analysis: there really is no one-size-fits-all solution to hydration, but your pee will tell you if you need to drink more

Despite its importance, water is also referred to as a forgotten nutrient. This is reflected by inconsistencies between water intake recommendations across different jurisdictions. These recommendations generally represent intakes to prevent ill-health (adequate intakes) rather than intakes to optimise health and performance.

This often results in confusion among the general public and causes the frequent question: how much water should I drink daily? The easy answer is 'well, that depends'! There really is no one-size-fits-all solution to hydration and this is more evident in elite sports performance than anywhere else. Using lessons learned from sport, here are some pointers about the need for a personalised approach to hydration.

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From RTÉ Radio 1's Today With Claire Byrne, dietitian Sarah Keogh on how much water really need to consume every day

The key is in the term here – these guidelines are general and intend to meet the fluid needs of most people, most of the time. Look at this sample of what is recommended by different authorities

Irish Heart Foundation: women should drink about 1.6 litres and men about 2 litres of water per day. That's about eight glasses of 200ml each for a woman, and 10 glasses of 200ml each for a man

HSE: a minimum of 1.2 litres of water per day

Food Safety Authority of Ireland: 8-10 cups of fluid every day

NHS: 6 to 8 cups or glasses of fluid a day

Association of UK Dietitians: Men - 2000ml; women -1600ml

The consensus seems to be to aim for a minimum of 1.2 litres daily and anything up to 2 litres might be beneficial. Daily fluid intakes should mostly constitute water, with a nod to the benefits of milk, fruit juices, and an acknowledgement that caffeinated beverages and alcohol should be kept to a minimum.

It is important to acknowledge that the literature for general recommendations reflects investigations on adult men. There is little or no information on older adults, who may be at particular risk of dehydration, or women and there has been little attempt to consider hormones that influence kidney functioning. That said, there is unlikely to be any great deviations on a population basis.

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From SciShow, one of the world's most asked questions: how much water should you drink?

The average daily total water intake for Irish adults is reported at 2.3 litres per day (males 2.5 litres; females 2.1 litres). There are some groups identified as more likely to be at risk from lower than recommended intakes, namely older adults, those with high body mass and fat mass. Otherwise, it seems that we are meeting the general population based guidance for daily fluid intakes. So what is all the fuss about?

The population-based guidelines aim to prevent ill-health in most people most of the time, and it appears that many Irish adults meet the recommendations. Where does this leave those with higher fluid requirements, those active population and those more at risk of dehydration (older adults)? What are the consequences for those who do not meet recommendations?

When dehydration reduces body mass by over 2% (worked example : usual weight 70 kg, acute weight loss associated with perspiration of 1.4kg, weight immediately post exercise = 68.6 kg = 2% reduction in body mass by dehydration), there are consistent reports that mood is influenced, fatigue is greater and alertness lower. This results from undesirable changes to the circulatory, respiratory and endocrine systems arising from dehydration. Scientific research tells us that sweat rates vary across sports disciplines with team sport athletes sweat rates reported at 0.7 – 2.6 litres per hour. It becomes clear that hydration requirements of specific groups will not be met by general guidelines.

Deviations from maximal performance associated with dehydration

In elite sports performance, an athlete's hydration status is monitored and managed in training and competition. There are many different instruments, tools and techniques that are used, but these are generally not necessary for recreational athletes or members of the public. There are also a host of different fluids recommended dependent on the requirements for carbohydrate or salts concurrent with fluids.

How can the general public benefit from these lessons learned in a sports context? Individuals, particularly those who are active, should monitor their own urine output. If the total volume, smell or colour indicates that you need to drink more (smaller than usual volume, stronger in odour and colour than usual), regardless of whether you have met the population indication of 6 cups for example – then you need to drink more!

A recent review concluded that studies generally reported a high sensitivity of urine monitoring as a diagnostic tool for detecting dehydration and supported the ability of this method to distinguish across categories of hydration status. There are, of course, caveats in interpreting urinalysis. If you consume multivitamins, medications, beetroot or asparagus regularly, you may need to consider an alternative method to assess your hydration status, as each of these can alter urine colour and smell.

I think most people accept that water is important for health and performance. There is very compelling evidence that sub-optimal hydration status can impact how you feel acutely as well as your long-term health. The take home message is that the general recommendations are guidelines and a more tailored approach involving assessment of fluid intakes, losses, activity loads and environmental considerations will give a more comprehensive picture for elite athletes. Interested recreational athletes and active individuals could consider urine assessment to tailor intakes to demands. Watch out for confusion arising from beetroot though!


The views expressed here are those of the author and do not represent or reflect the views of RTÉ