How Much Water Should You Drink a Day?

[ SETTING THE HYDRATION TARGET ]

"‘Eight glasses a day’ is a myth with no real basis — it ignores your size, your activity and your climate. A better answer scales to your body and your day. In the ONDA Biocomputer model, hydration is a homeostatic set-point your body defends well on its own; your job is to give it enough raw material and read the simple signals it sends back."

Section 1: How much you actually need

A practical baseline is about 35 ml of water per kg of bodyweight per day — roughly 2.4 litres for a 70 kg adult, 3 litres for a 90 kg one. Because about 20% of your water comes from food, the target from drinks is a little lower than your total need. Then adjust up for:

• •Exercise: ~350–700 ml per hour of activity (more in heat, more if you sweat heavily).
• •Hot climate / sweating: add a few hundred ml.
• •High caffeine or alcohol: a small extra allowance — alcohol especially is dehydrating.

The Water Intake Calculator turns your weight and day into a target. But the number is a guide, not a quota.

Section 2: Myths worth dropping

• •Coffee and tea don’t dehydrate you. The mild diuretic effect of normal intake is more than offset by the water they contain, so they count toward your daily fluid.
• •You can overdo it. Drinking very large volumes fast — especially during endurance events — can dilute blood sodium (hyponatraemia), which is dangerous. Spread intake out, and use electrolytes (not just water) for long or hot sessions.
• •Thirst works. For healthy adults, thirst is a reliable signal; you don’t need to force-drink on a schedule.

PROTOCOL: Read the Colour, Not the Clock

The Hack: Glance at your urine — pale straw means well hydrated, dark yellow means top up. Keep a bottle within reach and sip across the day.

The Logic: Urine colour is a free, real-time hydration gauge that beats any fixed daily quota, because it reflects your actual balance right now — losses, intake and all.

[ HARDWARE_VALIDATION ]

VALIDATION_DEVICE: Urine colour + thirst

METRIC: Consistently pale-straw urine, steady energy

STATUS: HYDRATION_BALANCED

Educational estimate, not medical advice. Some conditions require fluid restriction or have special needs — follow your clinician’s guidance.