Water is one of those things we take for granted. We're lucky in New Zealand to be able to do that. Most of us have access to excellent quality water for very low cost, straight out of our taps.
Despite that, we quite like to buy water. I remember in the 90s when I visited the US for the first time and was astonished to find a whole aisle of bottled water.
It wasn't long before that trend hit us too, and it's been with us ever since, for better or worse. The latter definitely applies if we think of all those unnecessary plastic bottles.
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These days you can find not only ordinary and spring water, but vitamin water, sports water, activated water, alkaline water, ionised water. There's even protein water. The newest trend in the US seems to be CBD - cannabis-infused water, believe it or not.
These so-called "functional" waters are a growing segment of the water market internationally, although there seems to be patchy evidence to back many of the claims they make.
But water, whether from the tap or a fancy bottle, is something we need to stay alive. We can survive a fair while without food, but without fluid in some form, we're in trouble after a few days. Water makes up 50 to 60 per cent of our body mass.
A loss of even 2 per cent means we'll become dehydrated. Water is crucial to every chemical reaction in our bodies.
That said, we don't actually need to be permanently attached to a water bottle all day to get the hydration we need. The old "eight glasses a day" rule is a bit of a myth; no-one really knows where it came from. In reality our water needs vary from person to person, and from day to day; it depends on where we are and what we are doing.
If we're in a hot climate, or doing lots of exercise, we'll need more water than when we're in an air-conditioned office sitting still.
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Most of us need a basic intake of 2-3 litres to replace the water our bodies lose through the day. This might be where the 8 glasses thing came from.
A good way to know if you're getting enough water is to take a look at your pee: a pale straw colour means you're good.
Listening to your body in other ways will make sure you're hydrated, too; thirst is an obvious sign you need a drink, and it might also help if you're tired and headachey.
We don't have to get all of our water from water. We get it from other fluids, too, including milk, soft drinks, juice, coffee and tea.
You might have heard these last two are dehydrating, but that's a bit misleading. Though coffee and tea can have a mild diuretic effect, they still contribute to your water intake.
What most of us don't need are sports drinks. Though the All Blacks are sponsored by a sports drink company, even they probably don't drink these very often.
Those of us who're doing an average workout or playing sport don't need a sports drink to rehydrate, and most of us probably also don't need the extra calories they contain. Some sports drinks can be shockingly high in sugar.
Unless you're doing real endurance sports - several hours of activity – water is just as good to rehydrate.
We also get water from food. Most fruits and vegetables contain lots of water, for example; even unexpected foods like bread can be high in water.
When we're well-hydrated, our bodies can function as they should. If we're dehydrated our whole system, including our metabolism, slows, as our circulation slows down; our cells are not getting enough oxygen.
That might mean we also experience tiredness and "brain fog". Getting enough water gets things moving again.
Having plenty of water means our kidneys can do their job and flush out the impurities that are a by-product of metabolism. And water helps keep things moving through our digestive system and prevents constipation.
Water may help regulate our appetite, too. Drinking water before and between meals may slightly increase the calories burned and decrease the calories we take in when we eat.
There is not much evidence that water helps us burn fat, appealing as that idea might be.
It is possible to drink too much water, and this can be extremely dangerous. Hyponatraemia is an electrolyte disturbance which can be caused by drinking excessive water, causing the body's sodium levels to become dangerously low.
Most of us are not at risk of that on a daily basis, though. Water – in whichever form you have it – is a great first drink of choice.