You're probably dehydrated
right now.
Here's the maths.

Why most people are walking around dehydrated

Dehydration isn't just for athletes or people sweating in hot climates. Chronic, mild dehydration - sitting at 1–2% below optimal - is extraordinarily common in the UK, and most people never connect the symptoms to water intake.

A 2015 study from the European Journal of Nutrition found that over 80% of UK adults don't meet even the basic European Food Safety Authority hydration recommendations. Not a rounding error - eight in ten people.

Here's the insidious part: once you're mildly dehydrated, your thirst mechanism becomes less reliable. You've essentially trained your body to accept a lower baseline. You stop noticing you're thirsty because you're always a bit thirsty. It becomes your normal.

The 1 litre per 20kg rule - your baseline

Forget the "8 glasses a day" advice. It's meaningless without knowing your bodyweight, activity level, or climate. The formula that actually makes sense:

This is your minimum - not your target on a hard training day. Exercise, heat, alcohol, and caffeine all act as diuretics, pulling water from your body and raising your requirements substantially.

Adjust for these factors

• Exercise: Add 500ml–750ml per hour of moderate exercise, more if you're sweating heavily
• Caffeine: Each cup of coffee or tea increases your requirement by roughly 100–150ml net (after the diuretic effect)
• Hot weather: Add 500ml–1 litre on days above 22°C
• Alcohol: Alcohol is aggressively diuretic - for every unit of alcohol, you lose approximately 100ml of water above what you drank
• Illness: Fever, vomiting, or diarrhoea can cause rapid fluid loss - increase accordingly

Signs you're chronically dehydrated

Most of these get attributed to other causes. They're actually dehydration:

• Afternoon energy slump - the 3pm crash many people have isn't blood sugar, it's often dehydration
• Persistent headaches - the brain sits in a fluid sac; when fluid drops, it can cause tension-type headaches
• Difficulty concentrating - even mild dehydration reduces working memory and attention span
• Feeling hungry after meals - the hunger and thirst signals share neural pathways; many people eat when they should be drinking
• Dark yellow urine - the simplest daily check. Aim for pale straw yellow throughout the day
• Dry skin and lips - skin is 64% water; dehydration shows up externally fast
• Constipation - your colon pulls water from stools to compensate for low intake, making them hard and difficult to pass
• Low blood pressure and dizziness when standing - blood volume drops with dehydration; standing up quickly causes a momentary pressure drop

The morning protocol - start every day hydrated

You wake up dehydrated. Eight hours without water, losing moisture through breath and mild sweating - you're typically 400–600ml down before you've even had a coffee.

Why the salt? Plain water in large quantities first thing in the morning can actually flush electrolytes too quickly. A small amount of sodium helps your body absorb and retain the water rather than sending it straight to your bladder.

Electrolytes - the part everyone ignores

Water alone isn't enough. Hydration isn't just about volume - it's about your body's ability to use the water you drink. Electrolytes (sodium, potassium, magnesium, chloride) are what allow your cells to actually absorb fluid.

This is why you can drink what feels like a lot of water and still feel sluggish, or need to urinate constantly. Without adequate electrolytes, especially sodium and potassium, the water passes through rather than being used.

Electrolyte sources

• Sodium: A small pinch of high-quality sea salt in water. Don't fear sodium if you're active and drinking adequate water - your kidneys handle it
• Potassium: Coconut water (genuinely excellent), avocados, bananas, leafy greens
• Magnesium: Dark chocolate, nuts, seeds, leafy greens - or supplement with magnesium glycinate
• Quality electrolyte products: LMNT sachets, Nuun tablets, Precision Hydration - all solid options without the excess sugar of sports drinks

Practical hydration - making it automatic

The biggest barrier isn't knowledge - it's habit. Here's how to make hitting your target automatic:

• Start with 500ml before coffee - non-negotiable. Put the bottle on your bedside table the night before
• Use a 1-litre bottle - not a glass. You lose track of glasses. Fill a 1-litre bottle and know you need to drink it twice (or three times) a day
• Drink before meals - 250–300ml before each meal. Helps digestion, reduces overeating, and gets liquid in without thinking about it
• Set a reminder at 3pm - the afternoon slump is often dehydration. A reminder to drink before reaching for a snack or coffee
• Cut off at 7pm - drinking heavily in the evening disrupts sleep with night-time toilet visits. Front-load your intake in the morning and afternoon
• Herbal tea counts - caffeine-free herbal teas (peppermint, chamomile, rooibos) contribute fully to your daily intake