Does Coffee, Tea and Soda Count Toward Water Intake?
Does coffee count as water? Yes. So does tea, so does soda, and so does the water in your food. If you drink four cups of coffee today, you have taken on roughly 950 ml of fluid, and almost all of it stays in you.
The belief that caffeine cancels out the water it comes in traces back to a 1928 study of three people. It has been tested many times since with better methods, and it has not held up.
What the caffeine research found
A 2014 trial at the University of Birmingham gave fifty habitual coffee drinkers either 800 ml of coffee or 800 ml of water a day for three days, then swapped them. Researchers measured total body water, urine output and blood markers. No meaningful difference showed up on any of them. The authors concluded coffee hydrates about as well as water when you drink it regularly.
A 2016 trial in the American Journal of Clinical Nutrition compared thirteen drinks and scored them on how much fluid was retained two hours later. Still water was the baseline. Tea and coffee scored within a few points of it. Milk and oral rehydration solutions scored higher than water, because the sodium and lactose slow how fast the fluid leaves the stomach.
Caffeine does have a mild diuretic effect, and it shows up most clearly in people who do not normally drink it, at doses above roughly 300 mg in one sitting. That is about four espressos at once. Regular drinkers build a tolerance to it within days.
What counts, and how much fluid is in it
- A 240 ml cup of coffee or tea: about 235 ml of water.
- A 330 ml can of soda: about 300 ml, plus 35 g of sugar you may not want.
- A 240 ml glass of milk: about 210 ml, and it is retained better than plain water.
- Food: roughly 20% of most people’s daily fluid, and more if you eat a lot of fruit, soup and vegetables. A cucumber is 96% water.
The one that does not count
Alcohol. Ethanol suppresses vasopressin, the hormone that tells your kidneys to hold water, so you pass more fluid than the drink contained. Each standard drink costs you roughly 100 ml net. Four beers in an evening leaves you down about 400 ml before the beer’s own water is counted back in, which is most of why hangovers involve a headache and a dry mouth.
How much do you need in total
The often-quoted eight glasses a day has no research behind it. The US National Academies suggest 3.7 litres a day of total fluid for men and 2.7 litres for women, from all sources including food, and those figures move with body size, activity and heat.
Skip the average: put your weight and training hours into the water intake calculator and it will give you a figure built from your own numbers. Then subtract what you already get from coffee, tea and meals, because plenty of people are closer to the target than they think.
If you would rather understand the sums before trusting them, how much water you need in a day sets out where the 3.7 and 2.7 litre figures came from and why they are ranges instead of rules.
Thirst is a better guide than a count for most people
For a healthy adult who is not training in heat, drinking to thirst and checking urine colour works. Pale straw is fine. Dark amber means drink something. Completely clear all day usually means you are drinking more than you need. If thirst keeps slipping past you, seven habits that raise daily intake covers what works without an app. If thirst keeps slipping past you, seven habits that raise daily intake covers what works without an app. If thirst keeps slipping past you, seven habits that raise daily intake covers what works without an app. If thirst keeps slipping past you, seven habits that raise daily intake covers what works without an app.
The exceptions are worth naming. Older adults lose thirst sensitivity, endurance athletes lose fluid faster than thirst reports it, and anyone working outdoors in summer should drink on a schedule instead of on feel. What dehydration does to performance covers how small a deficit has to be before it starts costing you.
Sweat hard for more than an hour and plain water stops being the whole answer. Sodium losses matter at that point, which is what electrolytes and hydration is about.
Scope and correction note, 16 September 2026: the ranges quoted here come from the American Council on Exercise and from published research, and they describe averages, not any individual. Nothing on this page is medical advice. If a figure here is wrong, tell us and we will correct it and date the correction. See the editorial policy and medical disclaimer.