THE importance of water is drilled into everyone pretty much from the moment they're born.

But what does a tall glass actually do for the body?

Nutrition Australia senior nutritionist Aloysa Hourigan said the kidneys, bowel, skin and mind all benefited from adequate hydration.

Kidneys ensure there is a proper balance of minerals in the body, such as potassium and sodium.

"Having our body fluids in balance is part of what keeps us alive, normally our kidneys are responsible for keeping all those chemicals in balance,” she said.

Ms Hourigan said water could also help protect against constipation, especially among those with high fibre diets.

"Fibre can act like a big sponge and may not be helpful for regularity,” she said.

"For people prone to getting constipated, drinking more water can make a world of difference.”

Dehydration can also cause skin to look dry, while eyes can look hollow.

Ms Hourigan said lack of water could also affect brain function, making people feel fatigued and lacking in concentration.

The most dramatic consequence of this is feeling nauseous or fainting.

The amount of water required by the body varies from person to person.

But according to Ms Hourigan, about 1.5-2 litres per day is sufficient.

This includes all fluid-heavy drinks, such as weak cups of tea and milk.

With water making up a high percentage of the human body as the base for fluid in cells and blood in veins, Ms Hourigan said it was crucial to ensure dehydration was kept up to scratch this summer.