You may have heard you need to drink eight glasses of water a day, but is this true? Do some drinks rehydrate your body better than others? Find out more about why good hydration is important, how much fluid you really need, and the different ways to stay hydrated. 

Why is hydration important?

Around 60% of our body is water and it plays many important roles – from helping maintain a normal body temperature, to lubricating joints, carrying nutrients around your body, and helping to get rid of waste products.

Even though our bodies contain a lot of water, we lose a significant amount every day as urine, sweat and even through breathing. In fact, around 50% of the water we lose is actually through our skin and breath!

Being dehydrated (having reduced levels of water in the body) can leave us feeling thirsty, tired and can make it difficult to concentrate. Even mild dehydration due to heat or exercise can affect mental and physical performance. 

If not addressed, severe dehydration can have serious medical consequences. It’s important to make sure we replace all the water lost daily to keep ourselves in balance.

It might be helpful to know that water is not the only way we can get enough daily fluids. Some drinks such as milk have particularly good hydration properties and even the food we eat can play a role.

How much should you drink to stay hydrated?

Fluid requirements can vary a lot from one person to another and depend on various factors such as climate, amount of physical activity and even what you eat. So there’s really no ‘one size fits all’ solution.

For Kiwi adults, it’s recommended we have around 2 litres of fluids (8 cups) a day for women and around 2.5 litres (10 cups) a day for men. This includes all fluids such as water, milk and other drinks.  Interestingly, the total water recommendation is actually higher but around a quarter of the water we take in each day comes from food. And not just the obvious liquid or juicy foods - solid food contains some water too. Even the humble baked potato is almost 70% water!

Apart from keeping you hydrated, choosing foods with a higher water content can also help you manage a healthy body weight. This is because a higher water content in a food lowers its ‘energy density’ – providing more volume to keep you satisfied, with relatively fewer kilojoules (calories).  Examples of foods with a higher water content include soups, stews, fruit, vegetables, yoghurt and also foods that absorb water during cooking like pasta and rice.

Can you have too much water?

Sometimes you might need more fluids than normal – when it’s really hot or if you’re exercising and sweating a lot –  but it’s important to remember not to overdo it. Having too much water can be dangerous because it can upset the normal balance of electrolytes in your body. So don’t have more than 1-1.5 litres of water per hour at any time.

Is water the only way you can stay hydrated?  

Water is of course a great choice to keep you hydrated. However, a drink’s ability to hydrate is not just about how much water it contains. Other factors like carbohydrate and electrolyte content can also affect how much water your body retains. An excellent example of this is milk – a recent study suggests milk may be as effective as water for rehydration. This is attributed to milk’s unique nutrition bundle including protein, carbohydrate and electrolytes which together can help your body absorb more water, avoid excessive urination and improve water retention.

While sports drinks are good for their hydration properties, they are intended for people who do intense exercise for prolonged periods or across multiple sessions in one day. They might need the additional electrolytes and carbohydrates (sugar) to replace those lost during their workout. However, this isn’t necessary for most people going to the gym or playing sport because many sports drinks contain a lot of added sugars, which isn’t good for your teeth or your waistline if consumed often. 

Caffeinated drinks are sometimes thought to be dehydrating because of their diuretic effect (increases the need to urinate). However, the caffeine levels usually found in drinks like coffee and teas (black or green) don’t really seem to have much of a diuretic effect at all – especially in regular caffeine consumers - so these drinks can still be good for hydration. Choosing a milky drink like a flat white or a chai latte is a great way to get in a bit of dairy nutrition too, which we now know is a great choice for keeping hydrated.