Hydration guides · 2026-08-10

How Much Water Should You Drink at a Desk Job?

Everyone quotes eight glasses a day. Almost nobody knows where that number came from, and it probably is not your number.

Where the eight glasses rule came from

The famous 8x8 rule, eight glasses of eight ounces, is a memorable slogan rather than a finding tailored to you. Bodies differ. A 55 kg person in an air-conditioned office and a 95 kg person in a hot climate do not need the same amount of water.

It is a fine starting point if you currently drink almost nothing. It is a poor personal target.

A more useful starting point

A commonly used rule of thumb is around 30 to 35 ml of fluid per kilogram of body weight per day, from all sources including food. For a 70 kg person that lands roughly between 2.1 and 2.5 litres.

Adjust upward when

• It is hot or humid. You lose more through sweat even sitting still.
• You exercised. Add fluid to match what you lost, not a fixed amount.
• You are in dry air. Air conditioning, heating and flights all pull moisture out of you.
• You drink a lot of coffee. Coffee is not the dehydrator it is rumoured to be, but if it replaces water in your day, your total intake drops.

The simplest self check

Rather than obsessing over millilitres, most people can use a simpler daily signal: pale straw coloured urine generally suggests adequate hydration, while consistently dark yellow suggests you could drink more. It is crude, free and available all day.

Spread it out, do not cram it

Drinking two litres in one sitting is not the same as two litres across a working day. Your body handles a steady supply far better than a flood. For desk work this is the practical takeaway: small amounts, regularly, roughly a glass an hour during your working window, rather than a panicked litre at 6 pm.