Is Drinking Plain Water Enough? The Science of Optimal Hydration

 

We explore some of the common queries and misconceptions around drinking water and hydration.  

How much water do we really need to drink each day?

You only need to look around at the amount of Stanley water bottles in hand these days to know that being properly hydrated is on everyone’s mind. The amount of water a person needs can vary significantly based on several factors, including age, gender, activity level, pregnancy, climate, and overall health. The commonly cited recommendation is around 2 to 3 litres (about 8 to 12 cups) of water per day, but this is a general guideline and not a one-size-fits-all rule. 

If you’re someone who decided to rapidly increase their water consumption one day, be aware that this can lead to electrolyte imbalance, particularly “hyponatremia” (low sodium), which can be dangerous. It can also cause digestive discomfort, such as bloating or upset stomach, and lead to frequent urination, disrupting daily activities. Additionally, sudden high intake may temporarily strain the kidneys as they adjust to the new fluid balance, especially in individuals with existing kidney conditions.

If you’re not a big water drinker, focus on increasing your intake gradually and listen to your body's signals. Aim for hydration that aligns with your activity level and environment, being mindful of additional water on days you’re training hard or perhaps working outdoors on humid days, and remember that water from food sources counts toward your total fluid intake. If you’re someone who doesn't like the taste of water, consider adding lemon slices, herbal teas, frozen berries, fresh mint or cucumber to your water bottle.  

Can’t I just drink plain water to stay hydrated? 

There are some factors to keep in mind - for most individuals, plain water is adequate for general hydration alongside a healthy, balanced diet that meets basic nutritional needs. However, for individuals who are sweating heavily and losing vital electrolytes (in every droplet of sweat) that help with fluid balance (some people can lose half a teaspoon of sodium per hour!), they need to ensure they are replenishing these minerals in order to help prevent against symptoms of heat stress, such as cramping. We explore some lifestyle factors where extra electrolytes should be considered below. 

Did you know if you have been recently or frequently ill with a viral infection (e.g. Covid19 or Influenza A), you may also need more electrolytes due to the body’s response to infection such as heightened inflammation, fever and sweating, all factors that dehydrate the body. Maintaining adequate electrolyte levels supports recovery by helping regulate hydration, muscle function, and overall metabolic processes, making replenishment essential post-illness. 

 

When plain water may not be enough 
  • High intensity exercise 

  • Working in hot and humid environments 

  • Extended endurance activities (Running marathons) 

  • Heat stress 

  • Illness (viral infection) 

  • Menopause (hot flushes, night sweats) 

  • Dietary insufficiency (low electrolyte intake) 

  • Regular saunas 

 

We get salty about salt water in the morning!

While the social trend of drinking salt water upon waking claims several benefits, many of these assertions lack factual accuracy and scientific support. Sodium chloride is indeed a beneficial electrolyte that aids in fluid balance and hydration, and certain types of unrefined salt can contain trace minerals, beneficial for health. However, this trend has been overhyped and is generally unnecessary. 

There’s no harm in trying it, but for optimal hydration and health, it’s better to stick with plain water or specially formulated electrolyte solutions, especially during intense exercise or in hot conditions. It's also wise to obtain healthy levels of sodium through your diet. In the mornings, you can easily replenish sodium by adding natural sources to your meals, such as Celtic or Himalayan salt, or sprinkle freeze dried bone broth to your veggie omelette. Starting your day with a cup of hot bone broth may offer even more digestive benefits, as well as the sodium. After all, who wants to chug down a glass of plain salty water first thing in the morning? 

Is drinking cold fluids bad for hydration? 

It is a common misunderstanding that chilled or cold beverages will delay fluid absorption (and rehydration) due to the perception that the body takes longer to bring it to body temperature before absorbing. Research looking into this theory has shown cold/cool water has minimal negative effect on gastric emptying and delaying of fluid absorption.1 In fact, cold or chilled beverages has the added benefit of reducing against heat stress by helping to cool your body faster through helping to lower your core temperature. 

What is better for hydration – drinking 1L of water at once or smaller increments? 

It’s disgustingly hot and humid, temperatures soaring and you’re feeling thirsty, you guzzle down a full bottle of cold, delicious water. Chances are, you’re actually more likely to urinate out more fluid, than what you’re absorbing. If you consume a large volume of water at once (a tummy full of fluid), the body’s protective response kicks in and causes diuresis – to excrete a larger proportion through urination. Drinking smaller, more consistent amounts over the course of the day is recommended to support hydration – the rate in which the body absorbs water is around 1L per hour, sipping 250 ml every 15 minutes where heavy sweating is occurring rather than chugging that huge amount at once. 

Will high sugar or high carbohydrate drinks hydrate me faster than sugar free drinks? 

Even though these usually taste delicious (thanks to a heap of sugar!), they could be hindering your hydration. Beverages with a high glucose or carbohydrate amount are considered ‘hypertonic’, which means a high concentration of particles dissolved in water vs the concentration of body fluids. When consumed, the body has to draw water from the bloodstream to dilute these solutes in the gut, which can lead to dehydration rather than hydration. This process can also cause digestive discomfort, as the gut may struggle to absorb water effectively while dealing with high concentrations of sugar. 

In contrast, sugar-free or low-sugar drinks that are hypotonic, allowing for quicker absorption and more effective hydration. So, while sugary drinks may taste good, they can hinder hydration and cause unwanted digestive issues. 

What affects how well your body absorbs fluids: 
  • Drinking too much at once 
  • Energy density (high sugar or high carbohydrate) 
  • Intense exercise - can slow gastric emptying rate, make sure you take adequate breaks to stay properly hydrated 

 

Did you like this article? Learn more about hydration here.

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