You know the scene. The day runs away with you, meetings stack up, you can feel you're thirsty, and you promise yourself a big glass of water 'later'. Except later rarely arrives. Sometimes you snack instead, and the feeling settles without your body having really had what it asked for. Repeated week after week, this small postponement starts to show — and the good news is that a few simple habits are enough to put things back on track.

What we know, and what we don't yet know

An adult's body is about 60% water, a proportion that varies with age and body fat. Every day, you lose water through urine, stools, breathing and sweat, and these losses need to be replaced by what you drink and what you eat.

What we know: dehydration, even mild, may show up as fatigue, difficulty concentrating, headaches or reduced tolerance to exercise. What we don't yet know precisely is the threshold at which each person feels these effects. Needs vary from one person to another and from one day to the next, depending on heat, activity, diet and health.

Glass carafe and water glass on a stone worktop, morning light
Water: a need that varies from day to day

Why ignoring thirst isn't a plan

Thirst is a useful signal, but it arrives late — and it isn't always reliable. With age, in children, when you're tired or in high heat, it can become blunted. The result: you drink less when your needs increase, which doesn't help.

Some situations are risk factors for dehydration: heatwave, intense exercise, fever, diarrhoea, vomiting, pregnancy, breastfeeding, or taking diuretic medicines. If any of these applies to you, prevention means more regular fluid intake and, if needed, medical advice.

How much to drink, and for whom

The idea of a single two-litre threshold circulates widely. Scientific guidance refers instead to total water, including drinks and food. The European Food Safety Authority (EFSA) suggests about 2.0 litres per day for an adult woman and 2.5 litres for an adult man, in temperate conditions and with moderate activity.

Some of this comes from food: fruit, vegetables, soups, yoghurt. There's no need to count every glass to the millilitre. But if you sweat a lot, are pregnant or are breastfeeding, your needs increase. And if you have heart or kidney disease, don't change your intake without speaking to your doctor: monitoring advice is personalised.

In practice, remember this: drink regularly through the day, without waiting for intense thirst. Pale yellow urine is a simple, useful guide. If in doubt, if you have unusual symptoms or a chronic condition, speak to a healthcare professional rather than self-prescribing a quantity.

What you drink matters too

Water remains the most suitable drink for hydration. In the UK, tap water is tightly regulated by the drinking water inspectorates; it costs far less than bottled water and creates no plastic. If you dislike the taste, chilling it in a jug or adding a few mint leaves can be enough.

Herbal teas, tea and coffee count towards fluid intake. Contrary to a common myth, their diuretic effect is modest at usual doses: current evidence suggests they contribute to hydration. Fizzy drinks, juices and sweetened drinks mainly add sugars, which are best limited. Alcohol increases water losses and remains a risk factor: moderation is the rule.

In practice: habits that stick

Keep a reusable bottle visible on your desk, in your bag or near the kitchen. Fill it in the morning and set yourself two or three points in the day to finish it. Add water-rich fruit and vegetables to meals and snacks: cucumber, tomato, watermelon, courgette, citrus fruit. And if you often forget, a phone reminder can make the difference.

The aim isn't to turn you into an accountant of every glass of water, but to make the habit easier than forgetting. A bottle you can see, a jug you refill in passing, a piece of fruit you bite into: small prompts that work for you without you having to think about them.

Budget

On cost, the difference is clear. Tap water costs a few pounds per cubic metre — less than a penny per litre, depending on your water company. Bottled water usually costs between around 20p and £1.50 per litre in supermarkets.

For a reusable bottle, expect around £15 to £40 for stainless steel or glass, and £20 to £50 for an insulated model. A filter jug often costs between £15 and £40, with replacement cartridges around £20 to £60 per year. Prices vary by material, capacity, brand, guarantee and where you buy: supermarket, hardware shop, zero-waste shop, pharmacy or online.

Choose a food-grade stainless steel or glass container, with a replacement seal available and a removable lid for cleaning. Consider what happens at the end of its life: glass and stainless steel are recyclable, while a plastic bottle scratches and needs replacing sooner. If tap water isn't drinkable where you are, bottled water remains a fallback, with the downside of packaging and transport.

Sources

  • World Health Organization, 'Drinking-water', fact sheet, 2023.
  • EFSA, 'Scientific Opinion on Dietary Reference Values for water', EFSA Journal, 2010.
  • NHS, 'Water, drinks and hydration' and the Eatwell Guide.
  • Drinking Water Inspectorate (DWI), information on tap water quality in England and Wales.
  • UK Chief Medical Officers' low-risk drinking guidelines.