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Comment by sa46 | Hacker News Reader

I used to be a logistics officer for an Infantry battalion.

Most of the comments down thread underestimate water consumption. Depending on the climate, you'll want the following daily quantities [1]:

- 2-3 gallons for drinking

- 1.5 gallons for hygiene (can skip for a while)

- 0.5 gallons for food prep

The planning factor for military operations was 8 gallons per person per day. Water is heavy—8 pounds per gallon—and acquiring, storing, and moving it is a large effort.

[1] https://cascom.army.mil/g_staff/g3/TTD/Products/QM-How-to-Ha...

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> 8 pounds per gallon

It never occurred to me that people needed this spelled out, but I guess it's simpler in most of the world where 1L = 1kg.

I don't think you can blame inch-pounds for this one- even though we rationally know it is heavier than most materials we don't "think of" water as heavy because modern society gives us the luxury of seldom having to handle more than a thirty minute or so supply of it at once.

I wasn't actually commenting on the "heavy" part but the "8 pounds per gallon" part. I can do these conversions on demand but, besides never being the native way I think personally, there are simply more numeric conversions you have to do when you use this system whether or not it's native to you.

then again, anyone with a garden or balcony that has to be watered with a watering can can [sic] attest to how heavy a little bit of water is. If you have a small 100m² garden and it rains a modest 1mm (per m² that is) that's 1L/m² equivalent to 1kg/m² or 100kg total mass of water. When it has rained 1mm people call it "three drops of rain" and they will have to water their plants anyway. That's already 10 cans @ 10L each to lug around.

The other kind of people who know about the weight of waters are people with campers / trailers and people with fish tanks in their apartments. The maximum allowable size for a fish tank in the middle of the room is not that much.

>> 8 pounds per gallon

> It never occurred to me that people needed this spelled out, but I guess it's simpler in most of the world where 1L = 1kg.

It's easy in gallons and pounds, too, if the correct gallon is used: 10 pounds per imperial gallon of water, by definition.

It's just as simple, frankly. A gallon is four quarts, each of which is two pounds of water. A quart is two pints: and a pint's a pound, the world round (Yes, most of us are aware of the irony of that couplet).

These are all things which are generally known to Americans. But HN has an international audience, for whom "gallon" is presumably somewhat vague.

> 8 gallons per person per day. Water is heavy—8 pounds per gallon

The average person needs far less than 65lbs (30kg) of water per day, which is a third of the average male weight in the US.

By medical standards humans need more like 8lbs (under 4l) per day for men and 6lbs (under 3l) for women. Less if your rationing and not exerting yourself.

OP’s factoring includes washing, food prep, all that other stuff.

1.5 a day for washing is hilariously wasteful. Use some wet wipes for crying out loud!

How do you wash your clothes and dishes with wet wipes?

Also you need to clean your home - you don't want to get sick in a catastrophe scenario.

1.28gal for toilet flushing the most efficient toilets. 1.6gal for normal and it can be worse for older ones.

I was on a hike that recommended 1 gallon to complete it for 5 miles round trip.

I’m sure there is a method to the madness of 8 gallons per person that isn’t easy to see. There is a lot of rounding up with the military also.

The normal amount in disaster preparedness is 1gal per person per day. The problem with the larger amounts is that people see they need huge amounts and don't do anything. Better to get started storing 5-7 gal for each person.

The way to allow for extras is to store water for a longer length of time. If recommended value is two weeks, and it is in my area, then a month is a good buffer.

8 ga of water per person per day is completely insane in disaster scenario. 2-3ga for drinking a day? Medical professionals recommend less than 1 for a normal person.

Keep in mind military operations generally aren't supposed to be disaster scenarios. And someone marching 10+ miles a day in full kit, possibly through heavy terrain or while under fire, is probably going to sweat a lot more than a normal person.

I’d you’re not doing anything. But if you’re doing physical effort then you’ll need to drink a lot more that 2–3L a day.

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