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How much water should you drink a day?
The honest answer is that a single daily number is the wrong unit. Your need is set by your body mass, your effort and your environment, and all three change between one day and the next.
Where the familiar numbers come from
The figures behind “eight glasses” or “two litres” trace back to population adequate-intake references — the US Institute of Medicine puts total daily water at roughly 3.7 L for men and 2.7 L for women, and EFSA gives similar European figures. Both are totals from all sources, food included, and both are averages across a whole population rather than prescriptions for one person.
Body mass is the largest single input, which is why the same advice cannot fit a 55 kg and a 95 kg adult. Age, sex, and pregnancy or nursing shift the baseline further, and any of those adjustments is bigger than the difference between six and eight glasses.
Then there is the day itself. A hot afternoon and a hard training session can each add more to your requirement than the entire baseline debate covers — which is why HydroPulse computes a baseline from your own numbers and then adjusts it continuously rather than handing you a fixed goal in the morning.
What HydroPulse does here
- A baseline derived from your weight, age and sex, not from a population average.
- Adjustment for pregnancy or nursing, which raise requirements measurably.
- Continuous adjustment for effort and weather instead of one morning target.
- A recommendation in millilitres or fluid ounces, so “how much now” has an answer.
- A history screen showing what the day actually came to, all sources logged by you.
How HydroPulse decides
- You enter your weight, age and sweat profile once. That sets your personal baseline loss — the water you lose just by being alive and breathing.
- The watch reads your heart rate continuously and converts it into a heart-rate-reserve fraction: how hard you are working relative to your own resting and maximum heart rate, not to an average person's.
- Local temperature and humidity are fetched anonymously and turned into a heat-index multiplier, because the same effort costs far more fluid at 33 °C and 70 % humidity than at 18 °C.
- Every drink you log is credited back to the ledger. When the running balance crosses your threshold, HydroPulse tells you — with a specific millilitre amount and the reason behind it.
What to expect
Expect a personal daily total that moves — often noticeably below the familiar two litres on a cool sedentary day, and well above it on a hot active one. Food contributes roughly a fifth of total water intake and HydroPulse does not try to estimate it, so its numbers describe what you drink.
Your balance as a dial, with the amount to drink now. 
One tap to log, one to snooze — the phone stays in your pocket.
Wear OS 3.0+. One-time purchase — no subscription, no ads, no account. The app interface is in English.
Common questions
Is two litres a day wrong?
It is not wrong, it is generic. It is a reasonable central estimate for total intake across a population, and a poor target for a specific person on a specific day.
Does food count toward the total?
Yes, roughly 20 % of total water intake comes from food in a typical diet. HydroPulse tracks drinks only, so its figures are deliberately about what you drink.
Should I drink to a schedule or to thirst?
For most healthy adults in ordinary conditions, thirst is an adequate guide. It becomes less reliable with age, in the heat, during hard exercise and when you are deeply focused — which is exactly the set of cases this app targets.
Can I set my own daily goal?
HydroPulse works from a balance rather than a goal, but the threshold setting lets you decide how far the balance may drop before it says something, which is the same lever in practice.
Where the model comes from
The baseline draws on IOM and EFSA adequate-intake figures, the sweat-rate component on ACSM exercise-hydration guidance, and the environmental multiplier on the US National Weather Service heat-index formula. These are population references adapted to what a watch can actually sense — a well-founded estimate, not a laboratory measurement.
Not a medical device
HydroPulse produces an estimate, not a measurement. It is a wellness tool, not a medical device, and it does not diagnose, treat or monitor dehydration or any other condition. If you take diuretics, restrict fluid on medical advice, or have a kidney, heart or endocrine condition, follow your clinician's intake guidance rather than this app's. Seek urgent care for confusion, fainting, or heat illness.
Private by design
Your heart rate, activity and drink log never leave the watch. There is no account, no advertising SDK and no product analytics — nothing tracks what you do in the app. Two things do leave the device: a pair of coordinates to a public weather service, with no identifier attached, and a crash report if the app fails. Neither carries your health data.
More on hydration
- On Wear OSA water reminder built for the watch, not a phone app with a complication.
- Running & trainingSweat-rate-aware reminders for runs, rides and gym sessions.
- Hot weatherWhen heat and humidity raise your needs, the reminders move first.
- At workFor desk days where six hours vanish between two glasses.
- Signs of dehydrationWhat mild dehydration actually feels like — and when it stops being mild.
- Heart rate & hydrationThe link between cardiac drift, effort and fluid loss.