Hydrate beautifully.
Your personal hydration and wellness companion.
A free Android app for tracking what you drink and building a healthier hydration habit, with no ads, subscriptions or paywalls.
Mia logs a litre of water and Hydra cheers up. (Mia is made up for these screenshots. Tap any image to see it full size.)
HydraHeart began with something personal. I've always understood the importance of staying hydrated, but knowing something is good for you doesn't necessarily make it easy to turn into a habit.
I wanted to drink more water, reach my daily goal and become more consistent. The motivation just wasn't always there.
So I tried existing hydration apps, hoping they'd make things easier. But I kept running into something that genuinely frustrated me: subscriptions and features locked behind payments.
Why should someone have to pay every month for tools that help them drink enough water?
I understand that software takes time, effort and resources to develop. But I've never believed that taking care of yourself should depend on whether you can afford another subscription.
So I decided to build something different.
HydraHeart started as a private project, something I was making purely for myself. I wanted a simple way to track my drinks, stay motivated and develop a healthier routine without advertisements, subscriptions or restrictions.
But as I worked on it, I started imagining what would make hydration tracking genuinely enjoyable. What if the app could encourage you? What if it felt alive? What if you could make it completely your own?
That idea became HydraHeart: a personal hydration companion with a little more character, a little more encouragement, and a lot of care behind it.
And somewhere along the way, I realised I didn't want to keep it just for myself. If it could help me build a better habit, perhaps it could help someone else too.
What began as a personal project became something I wanted everyone to have access to.
Because looking after yourself shouldn't come with a price tag.
Hydra isn't just a progress bar with a face. She's a little character who brings encouragement, personality and a bit of joy to your day. Every drink you log pours into her in its own colour. Every goal you reach, she celebrates with you. And the longer you spend together, the more she grows alongside your progress.
The same moment, with Hydra and in Focus Mode.
With Hydra, the app feels alive.
- Her face follows your day. She goes from concerned to content to happy to ecstatic as you get closer to your goal, and gets worried if you go over your caffeine or alcohol limit.
- She talks to you. What she says depends on the time of day, how far along you are, what you've just had and your streak. There are well over a thousand lines.
- She remembers. Hydra keeps track of the last couple of weeks, so she knows when you're on a roll and when you've had a rough patch.
- She grows with you. A necklace at Level 2, sparkles at 3, her diary at 5, a crown at 6, flowers at 7, a rainbow shimmer at 8, a butterfly at 9 and her golden legendary form at 10.
In Focus Mode, her face and speech bubbles disappear and you're left with a calm, distraction-free tracker: your goal, your progress and your numbers. Hydra is an invitation, not a requirement. Pick Focus Mode on day one or switch whenever you like. Neither is the wrong way to use HydraHeart.
Why the name? Hydra is short for hydration, and she's definitely got one head, not nine. (Give her a few levels and there'll be a crown on it.) Heart is what she is: the part of HydraHeart that cares how you're doing, not just how much you've had.
Hydration isn't one-size-fits-all, and neither is HydraHeart. Start with a daily goal worked out for you. Log the drinks you actually enjoy, whether that's water, coffee, juice or something else. Watch your progress take shape, look back at your habits, and let Hydra offer a little encouragement along the way. It all works together, so the routine feels natural rather than like another task.
Tap the big +, pick a category and add a drink. There are 70 of them in real sizes, from a 30 ml espresso to a litre of water, across Water, Coffee & Tea, Energy Drinks, Soft Drinks, Fruit Juice, Milk & Calcium and Alcohol. Each one knows its caffeine, sugar, calcium, alcohol and electrolytes.
Every drink also comes with an estimate of how much water it adds to your day. A litre of water counts in full, a 355 ml latte counts as about 283 ml, and alcohol, energy drinks and the stronger coffees show how much HydraHeart takes off your total before you add them. These are the app's own rough estimates for comparing drinks, not exact or medical measurements.
The numbers for every drink, a glass going in, and the moment you hit your goal.
Your body isn't average, so your goal isn't a flat 2 litres. HydraHeart works it out from your weight, how active you are and your climate, and Why this goal? shows you exactly how. Rather pick your own? Switch to Custom. You also get daily limits for caffeine, sugar and alcohol, and targets for calcium, sodium, potassium and magnesium.
Your goal and where it comes from.
How your goals are worked out
| Goal | How HydraHeart sets it |
|---|---|
| Water | 35 ml for each kg you weigh, plus 300 ml if you're lightly active, 600 ml if you're moderately active or 1 litre if you're very active. Add 600 ml for a hot climate or take off 200 ml for a cold one, then 10% less if you're over 65. It always stays between 1.2 and 5 litres. |
| Caffeine | Up to 400 mg a day, or 100 mg if you're under 18 |
| Sugar | Up to 50 g |
| Alcohol | Up to 16 g |
| Calcium | 1,000 mg, or 1,200 mg for women over 50 |
| Sodium | Up to 2,300 mg |
| Potassium | 2,600 mg for women and 3,400 mg for men |
| Magnesium | 320 mg for women and 420 mg for men |
If you choose "Other" for gender, the potassium and magnesium targets sit halfway between.
These numbers are general starting points for healthy adults, in line with common guidance (400 mg of caffeine a day, for example, is the figure the EFSA and the US FDA use). They don't take pregnancy or breastfeeding into account and aren't designed for children. HydraHeart is a wellbeing companion, not a medical device: if you're pregnant, under 18, or have a condition that affects how much you should drink, ask your doctor what's right for you.
HydraHeart isn't only interested in what you've been drinking. It's interested in how you're doing.
Once a day, check in with Happy, Calm, Okay, Tired or Stressed, add a note if you like, and Hydra answers in her own way. Over time your Mood Calendar becomes a colourful picture of the days you've had: the happy ones, the stressful ones and everything in between. Because taking care of yourself is about more than reaching a number.
The same Hydra on five different days, a check-in, and the calendar it builds.
Building healthier habits starts with understanding them. HydraHeart includes 41 short, friendly articles on hydration, electrolytes, caffeine, sugar, alcohol, skin, wellbeing and everyday habits. Discover something new with Today's Lesson, explore topics at your own pace, or put a dozen common myths to the test. They're there to make the basics easy to read, not to replace advice from a doctor.
History shows your day, week, month and year: your totals, your average drink, what you drink most and how often you hit your goal. From Level 5, Hydra keeps a diary too, with an entry for every drink, written by her, about you.
Your week, your month, and Hydra's diary.
Hydra can be your Bestie, a Slay Queen, a Soft Girl, in her Villain Era, a Zen Master or your Coach: same Hydra, completely different voice. Tell her you're tired and Bestie says "Rest is so valid Mia 💤", while Villain Era says "Tired? Rest now, scheme later 😈".
Two more are hidden. Cold CEO turns up when you've been consistently brilliant, and Heartbreak Era turns up when things have been hard and gets softer and more honest with you. When one unlocks, Hydra tells you herself and you choose whether to switch.
Eight attitudes, each in a theme that suits her.
When the hidden personalities unlock
- Cold CEO: ten days in a row at 90% or more of your goal, or a solid fortnight at 85% or more.
- Heartbreak Era: a week of missed goals, or a week of low water when your moods have mostly been tired or stressed.
Every drink, mood check-in, goal and trophy earns HP, and HP takes Hydra through ten levels, each with something new for her. There are 60 trophies, from your first sip to a month-long streak and a Perfect Day where you hit every goal without going over a single limit. Locked ones show how close you are, and nothing you've earned is ever taken away.
Hydra's ten levels, and a few trophies that have been earned.
Thirty themes. One HydraHeart. Entirely yours.
HydraHeart should feel like your space, so personalising it goes much further than a background colour. Every theme changes the whole atmosphere of the app, Hydra included. Choose from 18 light themes and 12 dark ones, from soft, dreamy pastels to rich, dramatic colours. Six are yours from the start, and the rest open up as you level up or earn certain trophies.
The same morning in all thirty themes.
Hydra herself can be a droplet, a bottle, a cup, a woman or a bra instead of a heart. She can wear any of twelve accessories, use one of eight speech bubble styles, or say lines you've written yourself. The Level 8 to 10 rewards each have their own switch.
Shapes, accessories and speech bubbles
Set as many reminders as you like, at the times that suit your day, and they arrive in Hydra's voice: not "Time to drink water", but things like "Your future self is texting you: please drink water". Pick from 50 messages, switch off the ones you don't like, write your own, and choose the sound.
I don't believe building better habits should mean being hard on yourself.
Some days you'll reach your goal. Other days you'll forget, get distracted, feel exhausted, or have far more important things to worry about. That's life.
Missing one day doesn't erase a month of progress. Your level, your HP, your trophies and your history stay exactly where they were, and only your streak starts counting again. You haven't failed, and you certainly don't need an app making you feel worse about it. Whether you're back after a day, a week or longer, Hydra won't tell you off. She's just glad you're here.
No guilt. No pressure. Just keep going.
HydraHeart is free because I believe it should be, not because I'm waiting for the right moment to charge you.
| The promise | HydraHeart |
|---|---|
| Free to use, forever | ✓ Yes |
| Advertisements | None |
| Subscriptions | None |
| Paywalled features | None |
| Donations | Only ever optional |
| Extra features for people who donate | Never |
I don't want you choosing between paying for a feature and missing out on something that could help you build a healthier habit. I don't want ads interrupting a moment of self-care, and I don't want the app to feel like it's always trying to sell you something. I want HydraHeart to help you hydrate. That's it.
And if HydraHeart grows, if more people use it, if keeping it going gets more expensive or more demanding? That doesn't change the promise. You're not responsible for funding the app just to keep using it.
There's no way to donate yet. If there ever is, it'll be completely optional, and it will never unlock features, remove limits or give anyone a better HydraHeart. Someone who never donates will always be just as welcome as someone who does.
Every feature. Every update. Every glass of water. Free, forever.
HydraHeart isn't on Google Play yet. It's on its way, and when it gets there the link will be right here. There are no APK downloads in the meantime.
The first time you open HydraHeart, Hydra helps you make the app your own. She asks your name, birthday, height, weight, how active you are and what the weather's usually like where you live, then shows you the daily goal she's worked out. You choose between the Full Hydra Experience and Focus Mode, and decide whether you'd like reminders. Nothing is set in stone: you can change all of it later in Settings.
Everything in Settings
| Section | What's in it |
|---|---|
| Your Profile | Name, birthday, gender, height, weight, activity level and climate |
| How We Feel | Your mood check-in and the Mood Calendar |
| Personality | Hydra's personalities, including any hidden ones you've unlocked |
| Hydra's Look | Face, speech, shape, accessories, level rewards, speech bubbles and your own lines |
| Daily Goals | Your goal, worked out or custom, and the limits for everything else |
| Calendar | Day or month first, a 12 or 24-hour clock, and which day your week starts |
| Reminders | Times, messages and the sound |
| Themes | All 30 themes |
| Units | Millilitres, fluid ounces or litres |
| General | Haptics, sounds, animations, battery-aware mode, reduce motion, keep the screen on, and the language |
| About | The version, what's new, the privacy policy and the terms |
HydraHeart speaks English (with US or UK spelling), German and Spanish.
No account. No analytics. No ads. What you log, your drinks, moods and notes, is kept in HydraHeart's private storage on your phone, where other apps can't read it. HydraHeart has no servers and doesn't have the internet permission, so it can't send any of it anywhere itself.
That doesn't mean nothing on your phone ever goes online. Android and Google Play services can use the network for their own jobs, and two of those touch HydraHeart:
- Your phone's own backup can include it. HydraHeart allows Android's standard app backup, so if backup to your Google account is on, Android may save HydraHeart's data and restore it when you reinstall or move to a new phone. That copy is handled by Android and Google, not by me, and you can turn it off in your phone's backup settings.
- The fonts come from Google Play services, which downloads them and keeps them on your phone. If they can't be fetched, the app uses the system font.
Uninstalling HydraHeart deletes what's on your phone, but not a backup Android has already made.
| Permission | What it's for |
|---|---|
| Notifications | Showing Hydra's reminders. Say no and everything else still works. |
| Alarms & reminders | Sending your reminders at the times you set |
| Run at startup | Putting your reminders back after your phone restarts |
| Vibration | The little haptic taps around the app |
If you're curious about how HydraHeart is made, this part is for you. It's a native Android app written in Kotlin with Jetpack Compose, and it runs entirely on the phone: there's no server, no account system and no network code.
| Language | Kotlin 2.2 |
| UI | Jetpack Compose (BOM 2024.12.01) with Material 3 and Material icons |
| Navigation | Navigation Compose |
| State | One AndroidX ViewModel holding Compose state |
| Storage | Jetpack DataStore (Preferences), with lists saved as JSON through Gson |
| Reminders | AlarmManager, plus a boot receiver that puts them back after a restart |
| Fonts | Playfair Display and DM Sans as Google downloadable fonts |
| Android | 8.0 (API 26) and up, compiled against API 36.1 |
| Build | Gradle 9.6 (through the wrapper) and Android Gradle Plugin 9.4 |
Hydra is drawn in code on a Compose Canvas rather than put together from image or animation
files. Her shape, her face and expressions, the layered colours of each drink, her accessories and
her level effects are all drawn fresh as you use the app. That's what lets her react the moment you
log a drink, change shape or theme, or reach a new level.
I'm not taking code contributions (pull requests) at the moment, because HydraHeart is source-available rather than open source (see the licence). Bug reports and ideas are very welcome, though, and they're the best way to help: open an issue and tell me what happened or what you'd love to see. Every idea gets measured against the promises above: free for everyone, no ads, no subscriptions and no guilt.
Hi, I'm Iri, the developer behind HydraHeart. This is my first app, and it's a project that means a lot to me.
When I first started building HydraHeart, I was building it for myself. I wanted to improve my own hydration habits, stay motivated, and have an app that worked the way I wanted it to. I never originally planned for it to become something I'd share with other people.
But as HydraHeart grew, so did my ambitions for it. What started as a little personal project became something I realised could make a difference to somebody else. And that's what matters to me now.
I don't measure HydraHeart's success in downloads, ratings or revenue. I measure it by whether it genuinely helps someone.
If just one person uses HydraHeart and it helps them drink more water, develop a healthier routine, or feel a little better in their everyday life, then sharing this app was worth it.
It doesn't have to reach thousands of people. It doesn't even have to reach hundreds.
One person is enough.
I don't expect anything in return. You don't owe me a donation, a five-star review, or even a thank-you. Knowing that something I created has made a difference to someone's life is enough for me.
HydraHeart may have started as an app for myself, but I hope it can become something meaningful to you, too.
Thank you for giving it a chance.
— Iri
I make HydraHeart on my own (I also make WardenOne), and I read every message myself.
- Found a bug? Open an issue and say what you were doing and what happened. A screenshot and what Hydra was doing at the time help the most.
- Got an idea? Open an issue and tell me about it.
- Just want to say hi? Email iri.devsupport@gmail.com or find me on Discord as
iri.dev.
There's nothing to pay for and no way to donate yet. The most helpful things right now are telling me what works and what doesn't, and sharing HydraHeart with someone who might like it.
Copyright (C) 2026 Iri. All rights reserved.
HydraHeart is source-available, not open source. You're welcome to read the code and build the app for your own personal use, but please don't copy, modify or redistribute it, publish it on an app store, or reuse parts of it in other projects without my written permission. The full terms are in LICENSE.
The fonts are Playfair Display and DM Sans from Google Fonts (SIL Open Font License). HydraHeart is built with Jetpack Compose and AndroidX, plus Gson (both Apache License 2.0). The emoji are your phone's own.
Thank you for looking after yourself. Now go and have a glass of water. 💜