Thumbnail water constants

This is not advanced physics, but I often find myself figuring things about water supply. Here are a few numbers that rattle around in my head (I've also verified them against my Thomas J. Glover Pocket Ref, which I carry in my briefcase with my Bible and pocket U.S. Constitution).

1 cubic foot of water weighs 62.4 lbs.

1 cubic foot equals approximately 7.5 gallons. (Glover says 7.48052)

A gallon of water weighs 8.3 lbs.

An inch of rain on a square foot is 1/12 of a cubic foot which equals 0.62 gallons.

An acre-inch is 0.62 X 43560 sq ft/acre = 27,007 gallons.

I knew a guy who was panicking about Y2k back in 1999. He bought a whole bunch of MRE food and 8 or 10 barrels, 50 gallons each, to store water. He spent thousands of dollars.

He stopped by one day and asked me what I was doing to prepare for water. I pointed to a 20 X 25 tarp. He looked confused. I showed him how I could lay out the tarp on our sloped lawn so that a rain would wash into a natural trough that could easily drain into buckets. We live in the Pacific Northwest, where you can count on a 1/2 inch rain easily in a month, and more in the winter.

1/2 inch on 500 square feet yields 155 gallons. I knew from sailing provisioning that a gallon per day per person is plenty if you are not exerting hard. Even if you only collected half of this in a month, you could keep two people going with minimal effort. If need be, I could dump the water in our extra bathtub for storage.

And the tarp was cheap.

I wasn't really worried even about the tarp. There were fresh water streams nearby. A bit of filtration and maybe boiling would be sufficient for water in an emergency.

Y2k was a bust, of course. I understand that there are bargains on those water barrels.

The tarp principle is useful for arid climates. 19 mil pond liner goes for around $0.50 a square foot. I saw a 1000 square feet of visqueen for around $100. I think of people in desert climates without decent supplies of water. But a region that gets a downpour once or twice a year could collect a lot of water inexpensively. I once did it experimentally on a small scale (300 square feet) in an area that received 9 inches of precipitation per year. After one good rainstorm I collected 120 gallons. Multiply that by 10 or 20 and you can maintain a family.

Useful snippets from "Household Arithmetic" (1920)

Here is a book every home should have:

Household Arithmetic, Katherine F. Ball, M.A., Vocational Adviser (sic) for Women, University of Minnesota; Miriam E. West, M.A. Girls Vocational High School, Minneapolis. J.B. Lippincott Co., Philadelphia & London (1920).

I ran across the book specifically looking for the calorie content of various foods. It is useful to know these things if you are trying to figure out how long you can survive if the grocery store closes for some reason.

Some factoids I noted:

Calories burned per pound of body weight per hour (p. 131):

Sleeping 0.4
Sitting quietly 0.6
Light muscular exercise 1.0
Active muscular exercise 2.0
Severe muscular exercise 3.0

The book gives a handy little example (p. 132):

EXERCISE VI

Problem.-Estimate the probable energy requirement of a stenographer, 28 years old, weighing 125 pounds, whose time is divided each day about as follows: Sleeping, 8 hours; sitting quietly at meals, reading, taking dictation, etc., 8 hours; at light muscular exercise, dressing, standing, walking, typing, etc., 6 hours; at active muscular exercise, playing tennis, etc., 2 hours. Use Table I.

8 X 0.4 Calories =3.2 Resting
8 X 0.6 Calories =4.8 sitting quitely
6 X 1.0 Calories =6.0 light activity
2 X 2.0 Calories =4.0 active

Total Calories per pound per day =18.

125 X 18=2250=total Calories per day.

Pages 135 and following give the energy value of various foods. I've saved the entire book simply for this information. Page 146 gives a thumbnail sketch:

Food Calories per lb.
1. Smoked ham 1635
2. Corned beef 1245
3. Oysters 225
4. Butter 3410
5. Entire wheat flour 1650
6. Rice 1620
7. Cheddar cheese 2075
8. Milk, whole 310
9. Buttermilk 160
10. Peanuts 1775

So our normal stenographer, who needs 2250 calories per day, could get by in a pinch with a quarter pound of pork and a bit over a pound of rice a day. Sure, it's spartan fare, but not too hard to store.

I'd suggest the book as a wonderful, free, resource.