PEOPLE who get much of their daily liquids from plain water rather than other beverages may have healthier diets overall, a study suggests.

Using data from a national health survey of more than 12,000 Americans, researchers found that people who drank more "plain water" tended to eat more fibre, less sugar and fewer calorie-dense foods.

The reverse was true of people who got much of their fluids from other beverages, according to a report of the study in the American Journal of Clinical Nutrition.

The findings do not prove that drinking water makes for healthier eaters, said lead researcher Dr Ashima K Kant, a professor at Queens College of the City University of New York. But, she told Reuters, they do suggest a connection — and a reason to encourage people to choose water over beverages.

The findings are based on 12,283 Americans age 20 and older who took part in a government health and nutrition survey between 1999 and 2006.

On average, respondents got one-third of their daily fluids from water, 48 per cent from other beverages and the rest from food.

In general, the more water people drank, the more fibre and the less sugar they consumed. They also had a lower intake of calorie-dense foods — a general marker of a healthier diet. Calorie density refers to the amount of calories in a food in relation to its weight; fruits and vegetables, for instance, tend to have a low calorie density. From a "purely physiological" standpoint, Kant noted, people can get their fluid needs from any source.

Drinking plain water, therefore, is not necessary, but it may be preferable, she said. As for how much water a person should drink, there is no straightforward answer — despite the popular belief that people need eight glasses of water per day.

As a general rule of thumb, Kant said, sedentary healthy adults can let their thirst be their guide on when to drink.

Reuters