Free hydration check

Water Intake Calculator

Eight glasses a day is a slogan, not a measurement. Find a daily target that fits your body, your training and the climate you live in.

The basics

How much water you actually need

There is no single number. What you need depends on your size, how much you sweat and where you live.

The National Academies put adequate total water intake at about 3.7 litres a day for men and 2.7 for women. That figure includes everything: plain water, tea, coffee, milk, and the water inside your food.

Roughly a fifth of your daily water arrives on a plate rather than in a glass.

Fruit, vegetables, soup and yoghurt all count. That is why this calculator works from the drinking share of the total rather than the whole figure, then adjusts it for your body, your training and your climate.

What moves the number

Four things that change what you need

Two people of the same weight can need very different amounts on the same day.

+400 Per training day Millilitres, roughly, to replace the sweat of a typical session
+15% Hot or humid weather You lose more through skin and breath, and humidity makes sweating less efficient
+8% High altitude Drier air and faster breathing raise losses, and thirst is often blunted
+0% Cold weather Needs hold steady, but thirst drops, so people routinely under-drink in winter
In practice

Making it easy to hit

Hydration is a habit problem, not a knowledge problem. Four things that solve most of it.

  1. Attach it to things you already do

    A glass when you wake, one with each meal, one before you leave the house. Five anchors gets most people most of the way without any counting.

  2. Keep it within reach

    A bottle on the desk gets drunk. One in the kitchen does not. This is the single change that works for the most people.

  3. Drink around training, not just after

    Some before, sips during, more after. Waiting until you are thirsty mid-session means you are already behind.

  4. Watch the colour, not the total

    Pale straw is the target. Dark means drink more; completely clear all day usually means you are overdoing it.

Read it honestly

What this number cannot tell you

  1. Coffee and tea still count

    The idea that caffeine dehydrates you does not survive contact with the evidence at ordinary intakes. A cup of tea contributes water like anything else.

  2. More is not better past a point

    Drinking far beyond need dilutes blood sodium, and in rare cases dangerously. The goal is enough, not maximum.

  3. Some conditions change the answer entirely

    Heart failure, kidney disease and certain medications come with fluid limits that override any calculator. If you have been given a fluid target, follow that one.

  4. Thirst is a decent guide, with exceptions

    For most healthy adults, drinking to thirst works. It becomes unreliable in older adults, during hard exercise and at altitude, which is where a target helps.

Where it leads

Hydration on a GLP-1

Appetite falls on GLP-1 medication, and fluid intake usually falls with it. Less food means less water from food, and people often forget to drink when they are not eating. Dehydration then makes the common side effects worse: nausea, constipation, headaches and fatigue all get sharper.

20% Of your usual water comes from food. Eating much less quietly removes it.
Sip Steadily through the day rather than in large amounts, which sits badly on a slower stomach.

If nausea, constipation or fatigue are making treatment hard to stay on, hydration is one of the first things worth looking at. Momentum Health 360 reviews your full history, current medications and goals, and tells you plainly what your options are.

Contact Momentum Health 360
Common questions

Hydration, answered

How much water should I drink a day?

The National Academies suggest about 3.7 litres of total water a day for men and 2.7 for women, including what comes from food. In drinking terms that is roughly 2.5 to 3 litres for men and 2 to 2.2 for women, adjusted for your size, training and climate.

Do I really need eight glasses a day?

Eight eight-ounce glasses is about 1.9 litres, which is a reasonable middle for a smaller, sedentary adult and short for most other people. It is a memorable slogan rather than a recommendation with evidence behind it.

Does coffee count toward my water?

Yes. At ordinary intakes, the mild diuretic effect of caffeine does not offset the fluid in the drink. Tea, coffee, milk and soft drinks all contribute, though water remains the option without sugar or caffeine attached.

Can you drink too much water?

Yes, though it is uncommon. Drinking far beyond need dilutes blood sodium, a condition called hyponatraemia, which can be serious. It usually shows up in endurance events rather than everyday life. Aim for enough rather than as much as possible.

How do I know if I am drinking enough?

Urine colour is the simplest daily check. Pale straw suggests you are fine; dark yellow suggests you are behind. Persistent thirst, headaches and afternoon fatigue are the other common signs.

Should I drink more on a GLP-1 medication?

Most people need to make a deliberate effort, because eating far less removes the water that normally comes from food, and lower appetite blunts thirst. Sipping steadily through the day also sits better than large amounts at once. Contact Momentum Health 360 to talk through what applies to you.

Keep going

Other tools that help

Hydration is one piece. These cover the rest.

TDEE CalculatorThe calories you burn in a day Calorie Deficit CalculatorWhat to eat, and how long it takes Protein CalculatorHow much you need to keep muscle BMI CalculatorWhere your weight sits today

Medical disclaimer. This calculator and the information on this page are for general educational purposes and are not medical advice, diagnosis or treatment. Fluid needs are estimated from general guidelines and cannot account for pregnancy, breastfeeding, kidney or heart conditions, or medications that affect fluid balance. Anyone given a specific fluid target by a clinician should follow that instead. Contact Momentum Health 360 about your individual health before changing how you eat, train or take medication.