Switching to a healthier diet can reduce an individual's water footprint by as much as 55%.
According to new research, turning vegetarian has the biggest impact, but even cutting down on meat gives a saving of at least 10%.
Shifting to a healthy diet is a "win-win situation", say researchers.
Citizens will be healthier and their food can be produced using less of one of our most precious natural resources - water.
"The main message is that if you shift to a healthy diet, be it with meat or without (vegetarian or pescetarian), according to your own preference, it's not only good for your health, but it's also very good for the environment in the sense that you reduce your water footprint substantially," said Dr Davy Vanham of the European Commission's Joint Research Centre, in Ispra, Italy.
Facts from the study
The water footprint from food consumption (domestic and imported food) per person per day is 2,757 litres in the UK, compared with 2,929 for Germany and 3,861 for France
Switching to a healthy diet with meat would reduce water consumption by 11-35%
A healthy pescetarian diet (meat is replaced with fish and pulses, animal fat is replaced with oils from crops) reduces water consumption by 33-35%
A healthy vegetarian diet (no fish or meat, oils from crops in place of animal fat) reduces water consumption by 35-55%.
Freshwater resources are already scarce, but the problem is set to get worse, due to population growth, changing lifestyles and climate change.
Public messages on saving water by taking shorter showers or turning off the tap when brushing teeth are well known.
But there is lower awareness of the amount of water used to produce food. Raising livestock uses up a lot of water. Oils, sugars and fats also require large amounts of water to produce, but growing fruits and vegetables is more water efficient.
"If you look at the numbers for the countries it goes to 3,000 - 4,000 litres per person per day; these are enormous amounts when you compare them with direct water use at home," said Dr Vanham.
The results were broadly similar in the three countries, confirming that people in Europe tend to eat too much red meat, sugar and fat, but do not eat enough fruit and vegetables, he said.
The research, carried out in the UK, France and Germany, is published in the journal, Nature Sustainability.
It is based on analysis of food-related water consumption for current and recommended diets (healthy diet with meat, healthy pescetarian diet and healthy vegetarian diet) down to the level of individual boroughs, in the most detailed study of its kind.
The authors acknowledge that encouraging people to change their diet is not straightforward and requires a number of interventions, from taxing unhealthy food to better food labelling.