For low-carb & keto
Keto Water Intake Calculator
Quick answer
On keto, drink toward the higher end of normal — about 3–4 litres (100–135 oz) a day for most adults — because cutting carbs releases stored water and flushes sodium. Start from 30–40 ml per kg of body weight, add for activity and heat, and pair the extra water with electrolytes to dodge “keto flu.”
Fine-tune
Your daily goal
of water a day · about 12.5 glasses or 6.5 half-litre bottles
- 3.1
- Litres
- 106
- Ounces
- 12.5
- Glasses
Pace yourself
Spread it across the day and ease off after 9:00 PM for better sleep.
Electrolytes? Not needed
For everyday hydration, plain water and a normal diet cover your electrolytes just fine.
A friendly estimate for healthy adults, not medical advice. Your needs rise with heat, exercise, illness, pregnancy, and some medications. Don't drink more than ~1 litre per hour.
Why keto changes your hydration
The ketogenic diet has a built-in diuretic effect. Carbohydrate is stored in your muscles and liver as glycogen, and each gram of glycogen is bound to roughly three grams of water. When you go low-carb, glycogen stores shrink and that water is flushed out — which is why people drop several pounds in the first week and why early keto can leave you unexpectedly thirsty.
The catch is that you don't just lose water — you lose the electrolytes dissolved in it, especially sodium. Lower insulin on keto also tells your kidneys to excrete more sodium. That combination is the real cause of “keto flu”: the headaches, fatigue, lightheadedness, and muscle cramps many feel in week one.
Water plus salt, not water alone
Drinking more plain water without replacing salt can actually make electrolyte symptoms worse by diluting what's left. On keto, the fix is both: hit your water goal above and add electrolytes — salt your food generously, and consider sodium, potassium, and magnesium from an electrolyte mix, especially in the first few weeks and around workouts.
As your body adapts over a few weeks, the diuretic effect settles and your needs ease back toward your normal weight-based goal. Until then, keep a bottle close and listen to thirst.
Frequently asked
How much water should I drink on keto?
Aim for the higher end of normal — about 3 to 4 litres (100–135 oz) a day for most adults on keto, because cutting carbs flushes water and sodium. Use your weight as a baseline (30–40 ml per kg) and add extra during the first weeks of 'keto flu'.
Why does keto make you lose water?
Your body stores carbohydrate as glycogen, and every gram of glycogen holds about 3 grams of water. When you cut carbs, glycogen drops and that bound water is released and excreted — the rapid 'whoosh' of early keto weight loss is mostly water.
Do I need electrolytes on keto?
Usually yes. Along with water, keto flushes sodium, potassium, and magnesium, which causes most 'keto flu' symptoms — headaches, fatigue, and cramps. Salting food and adding an electrolyte drink genuinely helps here, unlike on a normal diet.
Sources
- 1.U.S. National Academies (IOM/NAM), 2005 — Adequate total water intake of about 3.7 L/day for men and 2.7 L/day for women, including water from food and all beverages.
- 2.Mayo Clinic — General guidance of roughly 2.7–3.7 L of total fluids a day, with thirst and pale-yellow urine as everyday checks.