Water intake reference values: EFSA vs US/Canada

What an adequate intake is

Both sets of values are adequate intakes, or AIs, not RDAs. The National Academies use an AI when there is not enough evidence to calculate an average requirement.

An AI is based on experimentally derived intake levels or on approximations of observed mean intakes by a group of healthy people. In plain terms, it describes what healthy people typically take in, rather than a measured minimum.

Total water: drinks plus food

Both bodies count total water. That includes drinking water, beverages of all kinds, and the water contained in food.

The share from food is not trivial. The US/Canada report says about 80% of total water comes from drinking water and beverages, including caffeinated ones, and about 20% from food. A hydration page from the University of Las Palmas de Gran Canaria summarizes the EFSA values. It gives 20–30% from food and 70–80% from beverages. Under the US/Canada value for men, 20% of 3.7 L means about 0.74 L arrives with food.

The two sets of values

In 2010, the European Food Safety Authority set its dietary reference values for water. It considers 2.0 liters a day adequate for women and 2.5 liters for men. The European Commission had asked EFSA to update earlier European advice, taking into account new evidence and recent national and international recommendations. Public consultations in 2008 and 2009 informed the final opinions, and EFSA discussed the drafts with Member States' nutrition experts in September 2009.

In February 2004, the US and Canadian Dietary Reference Intakes for water were released by the National Academies. They give approximately 2.7 liters a day of total water for women and 3.7 liters for men. The release also states these as 91 and 125 ounces. The gap between the two references is 1.2 L for men and 0.7 L for women.

• EFSA 2010, men: 2.5 L (84.5 fl oz, 10.6 US cups)
• EFSA 2010, women: 2.0 L (67.6 fl oz, 8.5 US cups)
• US/Canada 2004, men: 3.7 L (125.1 fl oz, 15.6 US cups)
• US/Canada 2004, women: 2.7 L (91.3 fl oz, 11.4 US cups)

Why the two differ

Both are adequate intakes, which lean on what healthy groups were observed to consume. Different panels, populations and data sets therefore give different numbers, even for the same definition of total water.

Conditions matter too. The Las Palmas summary notes that the EFSA values apply only to moderate environmental temperature and moderate physical activity. The US/Canada release says people who are very physically active or who live in hot climates may need more water.

Neither body turns its value into a glass count. The US/Canada release says it offers no rule of thumb based on how many glasses to drink. It adds that most healthy people meet their needs by letting thirst be their guide.

What the calculator shows

The calculator needs only ‘Sex’ and lets you pick ‘Show in’ liters, US cups or fl oz. It shows both reference values side by side, so the difference is visible.

There is no weight-based formula. Both reference values are stated per day by sex, not per kilogram, so the calculator does not invent a weight factor. If you add your ‘Weight’, it also shows the common 30 and 35 ml/kg rules of thumb, labeled as such, next to the references. Climate and activity, as both sources note, shift real needs around the reference values.

The values are for healthy adults. They are not made for pregnancy, breastfeeding, kidney or heart conditions, or people under 18.