Online water reminder

Why a browser tab makes a poor water reminder

This tool works, and we built it as well as a web page can be built. It is still the weakest kind of reminder there is, and it is worth being clear about why before you rely on it for a day.

A web page has no life of its own. Its timer runs inside the tab, so it stops when the tab closes, when the browser quits, when your laptop sleeps, and when your phone locks. Even while it is open, browsers deliberately throttle timers in background tabs — Chrome and Firefox slow hidden timers to roughly one tick a minute and can freeze them entirely after a few minutes, precisely so that idle pages stop draining battery. That is why the timer above measures elapsed time from a saved timestamp instead of counting its own ticks: it can tell you a nudge was late, but it cannot make the browser wake up on schedule.

Web notifications help a little and cost something. They only fire while the page is alive, they need an explicit permission grant, and if you decline once, the page can never ask again — you have to dig into site settings to undo it. On iPhone, web notifications only work at all if you add the site to your home screen first. A phone app faces none of this: the operating system holds the schedule, and it fires whether the app is open, closed, or never launched today.

How often should you actually drink?

There is no clinical guideline that says “drink every 30 minutes”. What the evidence supports is more modest: spread fluid across the day rather than taking it in two or three large hits. Your kidneys can only process somewhere around 0.8–1.0 litres an hour, so drinking far faster than that does not hydrate you better — it mostly produces a trip to the bathroom, and at extreme volumes it is genuinely dangerous.

A practical way to pick an interval is arithmetic rather than science. Take your daily target, subtract what you get with meals, and divide across your waking hours. If you are aiming for eight 8 oz glasses across sixteen waking hours, that is a glass every two hours — a much gentler cadence than the 15-minute setting most reminder apps default to. If you work out, add fluid around the session rather than shortening the interval for the whole day. The water intake calculator will give you the daily number to divide up.

Reminders fail for a boring reason

Most people who install a water reminder stop noticing it within a week. The nudge arrives, you are mid-sentence or mid-meeting, you dismiss it, and after enough dismissals your brain files the alert under noise. This is ordinary habituation, and no amount of louder chiming fixes it.

Two things help. The first is anchoring: attach drinking to something you already do without prompting — every time you sit back down at your desk, after every coffee, at the top of every call. A cue that is already in your day survives longer than one imposed on it. The second is logging. Tapping the glass counter above turns a dismissed alert into a small piece of evidence, and a visible tally that is behind by mid-afternoon does more work than the alert that produced it.

How much of this is stored anywhere?

None of it leaves your browser. The interval, your goal and today’s count are kept in this device’s local storage — there is no account, no server, and nothing to delete elsewhere. That also means the tally is tied to this browser on this device. A different browser, a private window, or your phone will each start from zero, and clearing site data wipes it.

Do you need a reminder at all?

For most healthy adults, thirst is a competent guide, and pale straw-coloured urine tells you more than any schedule. Reminders earn their place in the specific cases where thirst is a poor signal: older adults, whose thirst response genuinely blunts with age; people working long shifts who go hours without a break; hot environments and hard training; and anyone whose clinician has asked them to hit a fluid target. If that is you, use a reminder that keeps running when the screen goes dark.