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Comment by perlgeek | Hacker News Reader

To get an idea of the scale: the average residential water usage is around 120 liter per person and day in Germany, around 300 in the US.

Assuming you get around 8 hours of operations out of such a box per day, that would be 3m² of land usage for the German usage, or 7.5m² / 80ft² for the US, per person. Doesn't sound great, but not too terrible either, compared to current land use (for housing, cars, infrastructure, agriculture, ...)

That's of course ignoring other water sources, and also that the hours of operation will vary wildly with weather and season.

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As soon as it gets scarce we will probably stop flushing our toilets with drinking water here in the Netherlands and Germany..

Yes, and watering plants with drinking water could also stop.

If your children end up living in a world where water is so difficult to source that something like this is required, then the average households will likely be a lot more frugal than just burning through 120 L a day.

we’re fatter so we need more water to bathe :)

Let's do the math (based on [1]):

If I weigh 85 kg and measure 185 cm (BMI 24.8, right at the edge between normal and overweight), my body surface to wash is 2.09 m². Let's assume a 3-minute shower at 15 liters per minute, so 45 liters of water. So 21.53 liters per m².

If my weight is 120 kg (140% of above) and I still measure 185 cm (between Obesity I and II), then my body surface to wash is 2.42 m², an increase of 0.33 m². Applying the same ratio as above, at 21.53 liters per m², I would need 52.11 liters of water (115% of above).

So a weigh of 140% results in a water consumption of 115%.

Qualitative argument is right, but the effect is not linear.

[1] https://stats.areppim.com/glossaire/body_mass_def.htm

That assumes time to wash is linear to surface area. It is harder for heavy people though to wash themselves tho, harder to reach everything including tools, more tools required, more time spent not actively washing while the water runs.

OTOH, the more sizable the body the less water it takes to fill the bathtub.

I need more time to shower when I exercise, probably could save a lot of water by shaving my head.

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