Hydration reminders that follow your body, not a timer
Most water reminder apps divide a daily goal by your waking hours and buzz on the quotient. HydroPulse runs a fluid-balance model on your watch — heart rate, activity and live weather — and tells you to drink when the balance actually drops.
Wear OS 3.0+. One-time purchase — no subscription, no ads, no account. The app interface is in English.
An hour at a desk in air conditioning and an hour running in August cost your body wildly different amounts of water. A fixed interval cannot tell them apart, so it is either nagging you when you do not need it or silent when you do — and both failures teach you to ignore it.
HydroPulse keeps a running ledger instead. Passive loss ticks down from your personal baseline; sweat loss is estimated from how hard your heart is working relative to your own resting and maximum rate; heat and humidity scale that estimate up. Every drink you log credits the ledger back. The alert fires on the balance, so on a cool sedentary day you will barely hear from it, and on a hot training day you will hear from it early.
It was built for the wrist rather than ported to it: a native tile, a watch-face complication, one-tap logging from the notification, and a recommendation that always names an amount and a reason instead of just saying “drink water”.
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.
Why it is not another reminder timer
- A running fluid-balance ledger, not a countdown — the interval between nudges changes with your day.
- Heart-rate-driven sweat estimate, using your own resting and maximum heart rate.
- Live temperature and humidity folded in through a heat-index multiplier.
- Every alert carries a millilitre amount and a plain-language reason: heat, exertion or baseline.
- Three urgency levels — mild, moderate, urgent — so a nudge and a warning do not look identical.
- Native Wear OS tile and watch-face complication: your balance at a glance, no app to open.
- One-tap logging straight from the notification, plus a 15-minute snooze.
- Quiet hours, so it does not wake you.
- mL, fl oz or Imperial units, and your own threshold.
On the watch
Your balance as a dial, with the amount to drink now. 
One tap to log, one to snooze — the phone stays in your pocket. 
What you actually drank today, not what you meant to. 
Your weight, units and threshold — the model fits you.
Hydration, situation by situation
- 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.
- 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.
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.