Skip to content
Back Back to Insurance menu Go to Insurance
Back Back to Holidays menu Go to Holidays
Back Back to Saga Magazine menu Go to Magazine
Search Magazine

How much water should I drink a day?

15 July 2020

Headaches, tiredness and constipation are just a few of the symptoms that can result from drinking too little water. Find out how much you need every day.

Glasses of water with lemon
By the time we feel thirsty we may already be slightly dehydrated

Take a good look at your body. Flesh, blood, bone, nails, hair and some gristly, squidgy bits that, luckily, you can’t see. All of it needs water to work well and feel good.

How much water is in our body?

'Just over half of our body weight, not including fat, is water. This reduces with age and/or increasing levels of body fat,’ says Dr Paul McArdle, Registered Dietitian and Chair of the British Dietetic Association (BDA) Diabetes Specialist Group. ‘That adds up to around 42 litres in a 75kg man, and a little less in a woman. Most of this is contained in our body cells. The rest is part of the fluid that surrounds cells and plasma, which transports nutrients, hormones, and proteins to parts of our body that need it.'

Need to talk to a GP from the comfort of your own home? Saga Health Insurance customers can talk to a qualified, practising UK GP 24 hours a day by phone. Find out more about our GP service.

What does water do for the body?

Water doesn’t just sit there; it’s busy, 24 hours a day, keeping the myriad complex processes in our bodies working. The fluids carry nutrients to cells and carry waste away, help most of the chemical reactions in our bodies take place, keep our temperature regulated and help keep our eyes healthy. They also pitch in with the vital lubrication of our joints and digestive and mucous tracts.

The levels of our body fluids are very tightly controlled. It only takes small changes in our fluid balance to make us feel unwell, and to make us ill.

Unfortunately it seems that we’re not terribly good at drinking enough, (and we’re not talking Chablis here). Fluid intake is influenced mostly by thirst. And the thirst response is extremely sensitive. We only need to be a few hundred mls short of our ideal water balance to feel thirsty. But thirst is ony part of the equation because when we drink we stop feeling thirsty before our body is completely rehydrated - in fact thirst can be one of the first signs of mild dehydration.

How do our bodies lose water?

We expel fluid from our bodies every day. Around 50% goes out in our urine – along with toxic waste products. About 47% is lost through our skin, although this does depend on how hot it is and how much energy we’re expending. The more we sweat, the more water we lose – go somewhere very hot for your holidays and you could lose 10 litres a day. We lose around 2% of our water in our faeces, and a very small amount through our lungs.

An average, healthy adult can lose almost 2.5 litres of water a day. And with the water you lose electrolytes – minerals like calcium, potassium and sodium - which help maintain your body’s fluid balance. Replace the lost fluids and electrolytes and you’ll be hunky-dory. It’s when you drink less than you expel that your body starts to dry out. And that’s when you experience your body’s reaction to dehydration.

What is dehydration?

Dehydration occurs when our bodies lose excess fluid. This can be to an illness, exposure to high temperatures, exercising or exerting yourself without topping up your fluid intake or use of diuretic medications.

Need to talk to a GP from the comfort of your own home? Saga Health Insurance customers can talk to a qualified, practising UK GP 24 hours a day by phone. Find out more about our GP service.

What are the signs of dehydration?

As well as feeling thirsty (although this isn’t always a reliable sign, especially in older adults and children), they may include some of the following signs symptoms of dehydration:

  • Dark-coloured urine
  • Headaches
  • Constipation
  • Confusion and irritability
  • Poor concentration
  • Dry mouth
  • Tiredness
  • Dizziness
  • Urinary infection

You only need to lose 3-4% of body fluid for the signs and symptoms of dehydration to occur. 

How can I tell I'm drinking enough? 

The most reliable way to check whether you’re drinking enough is to look at the colour of your urine. It should be pale yellow or light straw colour. If it’s dark or strong-smelling, you’re dehydrated. (This doesn’t apply to your first wee of the morning, when you’ve been without a drink for some hours.)

What are the causes of dehydration?

Dehydration can affect anyone, and it isn’t simply a matter of not drinking enough. Older people tend to be more at risk because they have a reduced thirst response, which means they just don’t feel as thirsty as they did when they were younger.  Some medications too - notably diuretics - can deplete the body's fluid levels as well as fever and excessive sweating.

Young children and people with chronic illnesses are also at increased risk. Sudden and severe diarrhoea, especially if accompanied by vomiting, a high fever and excessive sweating, can cause dehydration, as can uncontrolled or undiagnosed diabetes. Certain medicines, including some blood pressure medications, diuretics and antihistamines can also make you dehydrated.

How do I replenish my body's fluid balance?

If you are mildly dehydrated drinking more should do the trick. However, if you – or anyone else – suffers more severe symptoms of dehydration, such as being very thirsty, not urinating for eight hours, having visibly dried-up skin, or being dizzy and confused, you need to get medical help immediately. 

In older people especially, confusion caused by lack of fluids can be mistaken for more serious – and possibly permanent – mental decline, so it’s important to keep an eye on how much older friends and relatives are drinking.

Six common causes of forgetfulness

How much water should I drink a day?

So what should you drink, and how much should you have?

Men need 2000 mls a day and women 1500 mls of fluid a day to keep fluid levels healthy - that's six to eight glasses of liquid. If it’s very hot, you’ve been very active and sweaty, are ill with a fever, have had diarrhoea and/or vomiting, or take diuretics you’ll need to drink more to keep your stocks from running low.

Plain old tap water is perfect, but you don’t have to limit yourself to this. Milk, fruit and vegetable juice, squash and fizzy drinks will all add fluid to your system, although go easy on sugary soft drinks and limit fruit juice to one small serving a day. Tea and coffee do have a slight diuretic effect – the caffeine in them and in some fizzy drinks can make you produce more urine than other drinks. But in most cases it makes very little difference, so these drinks still help you stay hydrated.

Alcohol is a stronger diuretic, and drinks with a high proportion of alcohol, such as spirits, will increase your fluid loss, and add to the effect you feel the next morning, as dehydration is part of the cause of hangover symptoms, so intersperse with low-sugar soft drinks or water. Drinks with a low alcohol content, such as wine spritzers and many beers, won’t normally upset your fluid balance.


Unlimited access to a qualified GP with Saga Health Insurance - you'll have access 24 hours a day, 365 days a year to a GP consultation service. Find out more about our GP phone service.


Saga Magazine is supported by its audience. When you purchase through links on our site or newsletter, we may earn affiliate commission. Everything we recommend is independently chosen irrespective of affiliate agreements.

The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.