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Drinking water in hot weather
Humidity is the part people underestimate: when sweat cannot evaporate, your body produces more of it for less cooling. HydroPulse reads both temperature and humidity and shifts your reminders accordingly.
Why the thermometer alone is not enough
At 32 °C and 30 % humidity sweat evaporates and does its job. At the same temperature and 75 % humidity it runs off you instead, so you lose the fluid without getting the cooling and your body compensates by sweating more. The heat index exists precisely to capture that difference, and it is what HydroPulse feeds into the model.
Thirst is a lagging indicator in the heat. By the time it is insistent you are often already a percent or two of body mass down, and in hot conditions that gap opens faster than the sensation catches up.
Heat also raises your needs while you are doing nothing at all. A still afternoon on a balcony has a real fluid cost that no activity tracker registers, which is why the environmental multiplier applies to the baseline and not only to exercise.
What HydroPulse does here
- Live temperature and humidity, fetched anonymously from a public weather service.
- A heat-index multiplier applied to baseline loss, not just to workouts.
- Earlier and more frequent alerts on hot days, without you changing a setting.
- Coarse location only — enough for local weather, never precise tracking.
- A 30-minute weather cache, so the accuracy costs almost no battery.
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
On a genuinely hot day you will notice the app asking sooner and asking for more, and on a cool day it will go quiet. That contrast is the feature. Coarse location is optional — declined, the app falls back to a temperate default, which is safe but blunt in a heatwave.
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
Does it use precise location?
No. It requests coarse location only, uses it to look up local conditions, and does not store it. The request carries coordinates and nothing that identifies you or your watch.
What if I say no to location?
The app keeps working and uses a temperate default for the environmental component. Your heart rate and activity still drive the estimate; only the weather half is missing.
Can drinking too much be a problem?
Yes. Drinking very large volumes of plain water in a short time can dilute blood sodium, which is dangerous. HydroPulse recommends modest amounts spread through the day and is not designed to push you toward extremes.
Is it useful in a sauna or a hot workshop?
It will register the heart-rate rise, but it reads outdoor weather, so an indoor heat source it cannot see will be underestimated. Treat its number as a floor in that case.
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.
- At workFor desk days where six hours vanish between two glasses.
- How much per dayWhere the 2-litre rule comes from, and why your number is not that.
- 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.