Fasting & Water Consumption

Food Has a Water Footprint

Water is one of the less visible resources hiding behind food. Unlike a carbon figure printed on a label, water use rarely appears anywhere consumers can easily see it, even though it shapes nearly every stage of production.

Agriculture accounts for approximately 70% of global freshwater withdrawals, a figure commonly cited by organizations such as the FAO and the UN. That single statistic makes clear that decisions about food are, in a very real sense, decisions about water.

Water is used for:

• Irrigating crops in fields and greenhouses
• Watering livestock and cleaning animal housing
• Growing the feed crops that livestock consume
• Processing, washing and packaging food after harvest
• Cleaning equipment and facilities throughout the supply chain

Consequently, changing food consumption habits can potentially influence water demand, though the size and direction of that influence depends on specifics rather than being automatic.

Does Fasting Save Water?

The honest answer is: potentially, but indirectly, and not in a way that is easy to quantify precisely.

If fasting reduces total food consumption over the course of a year, fewer agricultural inputs — including water — may ultimately be required to produce that food. But the size of the effect depends heavily on which specific foods are being consumed, or avoided, on non-fasting days.

Water Footprint Is Complicated

Water use is not simply a smaller version of the greenhouse-gas story covered elsewhere in this series. A food can have a relatively modest carbon footprint while still carrying a significant water footprint, depending on how and where it is produced. Almonds, for example, are often cited as a crop with a comparatively high water requirement, despite being plant-based.

Local climate matters enormously. A crop irrigated in an arid region draws down water resources very differently than the same crop grown in a naturally wet climate, even if the total litres per kilogram look similar on paper.

Irrigation method matters too. Drip irrigation tends to be more water-efficient than flood irrigation, so two farms growing the identical crop can have very different water footprints.

Production intensity and choice of livestock breed or crop variety matter as well. Because of this layered complexity, environmental impact cannot be reduced to one tidy number, and anyone offering a single definitive water figure per food should be treated with some scepticism.

Fasting and Water: A Common Misconception

There is also a misconception worth correcting directly, because it comes up often in casual conversation about this topic.

Fasting, as practiced and discussed on this site, does not mean that a person stops drinking water. A food fast and a water fast are very different practices with very different physiological implications, and this site's project — 3 full days of food fasting per week across 52 weeks — is explicitly a food fast, not a dehydration exercise.

When discussing the environmental consequences of fasting, the relevant question concerns reduced food production and consumption, not withholding drinking water from the body. Conflating the two would misrepresent both the practice and the environmental argument.

A Broader Perspective

Fasting may potentially reduce the amount of agricultural water required to sustain a person's diet, but only if it genuinely reduces total food demand rather than simply shifting the same quantity of food into fewer eating days, as sometimes happens when people overcompensate after a fast.

Dietary composition can be just as important — or arguably more important — than fasting duration alone. As discussed in Fasting vs Plant-Based Diet, choosing lower-water-footprint foods on the days one does eat could plausibly have a larger effect than the act of skipping meals by itself.

The environmental equation, then, is not a single variable but a combination:

How much do we consume?

plus

What do we consume?

plus

How is it produced, and where?

Each of those three questions pulls on water resources differently, and none of them can be answered by looking at fasting frequency alone.

Blue, Green and Grey Water

Researchers studying agricultural water use often distinguish between three categories: blue water, drawn from rivers, lakes and groundwater; green water, meaning rainfall stored in soil and used directly by plants; and grey water, the volume theoretically needed to dilute pollutants released during production back to safe levels. This distinction matters because a crop relying mostly on rainfall in a wet climate places very little strain on scarce blue-water resources, even if its total water footprint, including green water, looks large on paper. Two foods with identical total water footprints can therefore have very different real-world consequences for local water stress, depending on which category dominates.

A Practical Illustration

To make this more concrete, consider a simplified comparison. A food produced almost entirely using green water in a naturally rainy region places relatively little pressure on local communities or ecosystems that depend on rivers and aquifers. The same crop grown as an irrigated export commodity in a semi-arid region, drawing heavily on groundwater, can contribute to genuine water scarcity even if the two crops look identical on a supermarket shelf. This is part of why blanket statements like "avoid water-intensive foods" can be misleading without knowing where and how the food was actually grown.

For someone practising periodic fasting, this complexity doesn't change the basic logic that eating less, on balance, likely requires fewer total agricultural inputs. But it does suggest that anyone wanting to meaningfully reduce their water footprint should pay attention to sourcing and production method, not just to overall food quantity.

Key Takeaways

• Agriculture is responsible for roughly 70% of global freshwater withdrawals, according to commonly cited FAO estimates.
• Water footprints vary by crop, irrigation method, climate and production intensity, not just by food category.
• A food can have a low carbon footprint yet a comparatively high water footprint, or vice versa.
• Food fasting and water fasting are distinct practices; this project concerns the former.
• Reduced food consumption may lower water demand indirectly, but the effect depends on which foods are involved.
• No single number can capture the full water story of a food; local context matters greatly.