The 30 Day Water Challenge, Built on Your Own Daily Goal

In metric, Priya's goal is 1,700 ml and Tom's is 2,800 ml. The gallon is 2.2 times her goal and about 1 L more than his.

Coffee, tea and milk count toward the target, so do not set yourself a plain-water goal on top of them. The NHS counts water, lower-fat milk, tea and coffee as part of your daily fluid; does coffee count as water has the details.

The 30-Day Plan, Week by Week

We ramp up over two weeks instead of starting at the full goal on day 1, so the extra bathroom trips arrive a little at a time. The plan holds the goal for the last two weeks and adds one cue at a time.

Priya's example, with her 1,700 ml goal and a first-week count of about 1,000 ml a day:

Days 1 to 7, Count and Add One Glass

Count everything you drink for the first three days without changing it. Then add one 250 ml (8.5 oz) glass tied to something you already do, such as the kettle in the morning.

Measure your usual glass and bottle once this week. How to track water intake covers the quick ways to do it, from a tally on a sticky note to counting refills.

Days 8 to 14, Fix the Work Hours

For many people the gap sits in work hours. Add a refill point when you sit down and another after lunch; our page on drinking more water at work lists the ones that stick for desk jobs and long shifts.

Days 15 to 21, Reach the Full Goal

This is the hardest week. The extra glasses now land in the afternoon, when drinking often stops.

Set one reminder for the time you usually forget. The steps for iPhone, Android and Apple Watch are on setting a water reminder on your phone, and the best time to drink water shows which moments matter most.

Days 22 to 30, Let the Cues Take Over

Keep the target and start removing help. Turn off one reminder every few days and see if the day still adds up.

If plain water is what makes you stop, now is the time to change the drink, not the goal; our ideas for drinking water when you don't like it keep the fluid up without the boredom.

Is the 30-Day Water Challenge Safe?

For healthy adults, yes, when the target is your own goal and you spread it through the day. The risk comes from drinking a lot fast, and two hourly limits mark where it starts.

0.7–1.0 L

an hour, the most healthy kidneys clear

1.4 L

(6 cups, 48 oz) an hour, the NIOSH cap for work in the heat

The US National Academies tie water poisoning to drinking faster than the kidney's "maximal excretion rate". NIOSH sets its cap for workers in the heat, who sweat part of that water out again.

Three rules keep the month safe:

• Never make up a missed day by drinking yesterday's shortfall today.
• Never finish a bottle in one go to "catch up" in the evening. A glass with dinner and one after is the most the evening needs.
• Stop raising the target once you reach your goal. More is not better past that point.

What Happens if You Drink More Water for 30 Days?

You pee more, especially in the first week or two, and your pee turns paler. If you were drinking too little before, dark yellow pee should give way to pale. We found no trial showing weight loss, clearer skin or a faster metabolism from a month of extra water, so we make no such claim.

Here is what you can expect, and what the evidence says about it:

• More bathroom trips. Most people pee about seven to eight times a day, and going more often "may still be normal" when you drink lots of fluids, Cleveland Clinic notes.
• Paler pee. The NHS check is "a clear pale yellow colour"; that is the sign the month is working.
• Some bladder urgency. In a two-year kidney stone trial of 1,658 people, the group pushed to drink more reported more frequency, urgency and night-time peeing at 6 and 12 months than the control group, but not at the later checks.
• A habit that fades if you stop paying attention. In the same trial, the gap in drinking between the groups shrank over the two years as the rewards tapered off, which is why days 22 to 30 hand the job to cues.

That trial was funded by the US National Institute of Diabetes and Digestive and Kidney Diseases and enrolled people aged 12 and over with kidney stones. It tells you about bathroom trips and follow-through, not about healthy adults' energy or skin.

What If You Miss a Day?

Start again the next morning at the same target and leave the day blank on the calendar. A month with 25 ticked days builds the habit; a month you abandon on day 9 because day 8 failed does not.

If you missed because the day was unusual, note why. A long flight or a day of meetings tells you where to put a cue next time.

Hot Days and Workout Days Need More

Your goal is an everyday number. On a hot day or a long workout you sweat out more, and the challenge target becomes a floor, not a ceiling.

For moderate work in the heat that lasts under two hours, NIOSH advises 1 cup (8 oz) every 15 to 20 minutes. Our guide on how much water to drink in hot weather covers heat waves, outdoor work and how often to drink when it is hot.

After Day 30

Keep the cues that stuck and drop the rest. From here, three small habits keep the month's work:

• Track one weekday a month. If it comes in more than a glass short, bring back the reminder for the hour you slipped.
• Move your last drink earlier if you wake at night to pee, as drinking water before bed explains.
• Keep the pace steady from morning to evening, as in how often to drink water, rather than saving the litre for after work.