Austere Survival

Clear water lies to you. A mountain stream running over clean rock can carry the same parasites as a stagnant pond, because the organisms that make you sick are too small to see and leave no smell. Treat every wild or storm-damaged source as contaminated until you have made it safe, and treat the clearest spring with the same suspicion as the muddiest ditch.

What treatment can and cannot do

The three field methods are boiling, chemical disinfection, and filtration, and each one targets living organisms.¹ None of them removes heavy metals, salts, fuel, or other chemicals, and none removes radioactive material.² If water is fouled by an industrial spill or runs off a battlefield, treating it for germs leaves the poison behind, so find another source.

Boiling — the method that fails the least

Boiling is the most reliable thing you can do, because it kills every disease organism normally found in water, whether the water is clear or cloudy.³ Bring the water to a rolling boil and hold it there for one full minute. Above 6,500 feet the air is thinner and water boils cooler, so hold the rolling boil for three minutes.¹

Pre-filter cloudy water first

Mud and floating matter shield germs from chemicals and feed the chlorine before it can disinfect, so cloudy water defeats bleach and iodine.⁴ Pour it through a clean cloth, paper towel, or coffee filter, then let it stand so the fine particles settle to the bottom.¹ Draw the clearer water off the top to treat. Filtering this way only clears the water; it does not make it safe to drink.

Chemical disinfection — unscented household bleach

When you cannot boil, plain unscented household bleach disinfects clear water. The dose depends on the strength printed on the bottle, so read the label before you count drops.¹ Add the bleach, stir, and let the water stand for at least 30 minutes.¹

After 30 minutes the water should carry a slight chlorine smell. If it does not, the bleach was used up fighting contamination; repeat the dose and let it stand another 15 minutes before drinking.¹

Iodine — tincture or tablets

Iodine is a strong disinfectant carried as a 2% tincture or as commercial tablets. For the tincture, add two drops to each liter of clear water; double it for water that is cloudy or stained, even after settling.⁵ Let it stand 20 to 30 minutes, and stretch that to 25 minutes or more in cold water, which slows the reaction.⁵ Purification tablets each free about 8 milligrams of iodine to treat one liter; use two tablets for cloudy or heavily polluted water, and follow the package time.⁵

Filtration — clears water, rarely finishes the job

A field filter strains out what is suspended in the water, and how small a thing it stops depends on how fine the filter is. A sand filter removes cysts, eggs, and cercariae and most visible matter, but it is unreliable against bacteria, so water that has passed through it must still be boiled or disinfected.⁷ A fine ceramic filter element, with pores about 1.5 microns or smaller, removes all the disease organisms normally found in drinking water — but only for a limited time before bacteria grow through it, so a ceramic filter is cleaned and boiled on a schedule.⁷ A charcoal filter pulls out excess chlorine and improves taste; it does almost nothing to germs.⁷

• Reject any source that may carry fuel, chemicals, or fallout — treatment will not remove them.
• Cloudy? Pre-filter through cloth or a coffee filter, then let it settle and draw off the top.
• First choice: rolling boil 1 minute, or 3 minutes above 6,500 feet.
• Bleach (unscented): 2 drops/L clear at 5–6%; double for cloudy; stand 30 minutes; confirm a slight chlorine smell.
• Iodine tincture (2%): 2 drops/L clear, double for cloudy; wait 20–30 minutes, longer in cold.
• After any filter, boil or disinfect before drinking unless using a tested fine ceramic element.
• Store treated water in a clean, covered, narrow-mouth container so you cannot recontaminate it.

Sources

1. CDC — Making Water Safe in an Emergency
2. EPA — Emergency Disinfection of Drinking Water
3. The Purification of Water on a Small Scale (WHO/IRC Technical Paper No. 3, 1973) — boiling section, p.5
4. EPA — Emergency Disinfection of Drinking Water (pre-filtering and settling cloudy water)
5. The Purification of Water on a Small Scale (WHO/IRC Technical Paper No. 3, 1973) — chlorine, iodine, and filtration sections, p.7–16
6. CDC — Making Water Safe in an Emergency (disinfectant limits vs. Cryptosporidium and Giardia)
7. The Purification of Water on a Small Scale (WHO/IRC Technical Paper No. 3, 1973) — sand, ceramic, and carbon filter limits, p.11–16

You can go weeks without food and only days without water, so water is the supply you plan around first. Finding it is half the problem; the other half is drinking it on a schedule that keeps you working, because the body gives you a poor warning when it runs low and no warning at all until you are already behind.

How much you actually need

At rest in mild conditions, an adult needs roughly 2.7 to 3.7 liters of water a day from everything eaten and drunk, with men at the higher end.¹ That figure is a floor, not a field number. Heat and hard work drive the need far past it, because every drop of sweat is water leaving your body to cool it.

Working in the heat, you replace what you sweat at roughly half a quart to a full quart per hour, climbing with the temperature and the load you are carrying.² A practical pace is one cup every 15 to 20 minutes, which lands near three-quarters to one quart an hour.³

Why thirst lags behind need

Thirst is a late alarm. By the time your mouth feels dry, you have already lost two to three percent of your body weight in fluid, and your ability to work has dropped even when you do not feel it.⁴ Studies that quieted thirst with small sips still measured the performance loss, which means the thirst signal and the actual shortage are two different things.⁴ So you drink to a schedule and to the heat, not to the feeling in your throat.

Recognizing dehydration

The early signs are the ones easy to wave off in the field: dark urine and less of it, a dry mouth, a headache, and a creeping tiredness. As it deepens, you lose focus and coordination, your heartbeat climbs, and the body stops sweating to defend its remaining water — which removes your cooling at the worst moment and opens the door to heat stroke. Treat the first dark, scant urine of the day as the signal to drink, before the harder symptoms arrive.

Water discipline

Discipline is the difference between rationing your sweat and rationing your water, and the first one is what keeps you alive. Cover up and keep your clothing on; bare skin sweats faster and burns, and clothing holds the cooling sweat against you longer.⁵ Work in the cool hours and rest in the heat of the day. When water is short, slow your effort to slow your sweat — you cannot drink your way out of overworking in the sun.

Drink steadily rather than in huge gulps, and keep drinking on your schedule even when you do not feel like it, because the saved water in your canteen does you no good once you have collapsed.⁵ Avoid alcohol and tobacco, which both pull water out of you and deepen the shortage, and never drink urine — it carries salt and waste that only worsen thirst.⁵

• Drink to a schedule and the heat, not to thirst — thirst means you are already behind.
• Light work in heat: about ½ quart per hour. Hard work in extreme heat: up to 1 quart per hour.
• Never exceed 1.5 quarts per hour or 12 quarts per day — overdrinking is dangerous.
• Check urine: pale yellow is good, dark yellow means drink now.
• Keep clothing on, work the cool hours, slow down to cut sweat when water is short.
• Skip alcohol and tobacco; never drink urine.

Sources

1. CDC / National Academies — adequate total daily water intake
2. US Army TB MED 507 — Heat Stress Control: fluid replacement rates and hourly/daily limits
3. CDC / NIOSH — Heat Stress: Hydration (drink rate and overhydration warning)
4. University of Arkansas — thirst is not the best indicator of hydration; performance drops at 2% fluid loss
5. Survival Water Procurement and Purification (Jiyani) — desert travel and drinking discipline

Run a wood stove with the damper shut and it burns its own walls to stay lit. The starving body does the same. When the calories coming in fall short, it begins consuming its own muscle for energy, and your strength and judgment go with it.¹ Food in the field is fuel for that fire, and the job is to match what you put in to what the work and the cold are taking out.

What the body needs by the day

A person at rest needs roughly 2,000 calories a day just to function at a minimum.¹ That is a survival floor, not a working ration. Real daily needs climb with effort and with cold.

What the body burns first

Carbohydrates are the body's first and easiest fuel, and plants are where you find them. Roots, greens, nuts, and seeds supply the carbohydrate and some protein that keep you moving, and they are quieter and safer to gather than game.¹ Meat is more nourishing and matters most in the cold, but it costs more effort to get; for an immediate meal, take the abundant catches first, such as insects, fish, and reptiles, while you set traps for anything larger.¹

Ration with discipline

You can last weeks without food but only days without water, so never ration water to stretch food.¹ In hot, dry country you may need up to three gallons, about twelve liters, of water a day, and you should not drink more than 1¼ quarts in any single hour.⁴ Always drink while eating, because digestion itself uses water.¹

• When food is short, a thin sugar-water mix, about two teaspoons of sugar per liter, can hold off severe dehydration for a week if you keep activity and heat loss low.¹
• Eat your full ration before hard work, not after, so the fuel is there when the effort comes.⁴
• Stretch food by lowering the demand: limit sweat-producing work in heat, and conserve body heat in cold, rather than starving the engine.

Salt and electrolytes

Sweat carries out salt as well as water, and replacing only the water leaves you weak. Eating all your meals normally covers the body's salt needs.⁴ In an extreme situation where it does not, mix about a quarter teaspoon of salt into a liter of water, a concentration the body absorbs readily.¹

Sources

1. US Army Survival Manual (FM 21-76, 2006) — 2,000-calorie minimum; body burning its own tissue; plants as carbohydrate, meat more nourishing, eat abundant catch first; water before food; sugar-water ration; 0.25 tsp salt per liter.
2. Merck Manual / Dietary Guidelines for Americans — estimated daily calories for adults by sex and activity level.
3. NRC, Nutritional Needs in Cold and High-Altitude Environments and Performance Nutrition for Cold-Weather Military Operations (PMC) — ~4,500 kcal/day cold allowance; 5,000–7,000 kcal/day arctic expenditure.
4. Field Hygiene and Sanitation (FM 21-10 / MCRP 4-11.1D, 2000) — up to 3 gal / 12 L per day in hot dry climates; do not exceed 1¼ qt/hr; eat all meals for salts; no salt tablets.

Your body cools itself the way a wet cloth cools a window: water on the skin evaporates and carries the heat away with it. Sweat is that water, and evaporating a single quart of it pulls about 600 calories of heat out of you.¹ Heat injury is what happens when that system runs out of water to spend or, worse, breaks down entirely. The two stages have different names, different signs, and one difference that decides whether a person walks away or dies.²

Heat Exhaustion: The Warning Stage

Heat exhaustion is the body losing water and salt through heavy sweating faster than they are replaced, until the blood pressure can no longer be held up.² The person is miserable but still working right on the inside. Look for headache, nausea, dizziness, weakness, irritability, hard thirst, and heavy sweating, with a temperature that is up but not soaring. The skin is the tell: it stays cool, moist, and clammy, and the sweat is still pouring.³

Treat it where it starts, before it climbs. Move the person into shade or cool air, lay them down, and raise the legs. Strip off heavy or tight clothing. Cool the skin actively — cold wet cloths to the head, face, and neck, or a spray of water with air moving over it. Give cool water or an electrolyte drink in frequent sips, never alcohol or caffeine. If they are not clearly better within 30 to 60 minutes, or if they get worse, treat it as the emergency above.⁴

Heat Stroke: The Emergency

Heat stroke is the cooling system itself failing. The body can no longer shed heat, the core temperature climbs out of control past 103°F, and the brain begins to cook.⁵ The signs are loud: confusion, slurred speech, staggering, seizures, fainting, loss of consciousness. The skin is hot, and it may be dry because sweating has shut down — or it may still be wet, especially when heavy exertion drove the collapse.⁶

For heat stroke, call for emergency help and start cooling at the same second — do not wait for the ambulance to begin. Move the victim to shade or cool air and strip the outer clothing. The fastest cooling is cold-water or ice-water immersion of the body; if that is not possible, soak the skin and lay cold wet cloths or ice on the head, neck, armpits, and groin while you fan air across them. Stay with the person until help arrives.⁷

Two milder problems sit alongside these. Heat cramps are painful spasms in the working muscles, driven by salt lost in sweat. Heat syncope is a brief faint from blood pooling as the heat widens your vessels. Both are signals to stop, cool, and replace water and salt before the next stage arrives.⁹

Prevention, Hydration, and Work-Rest

You cannot feel dehydration coming in time. Thirst lags behind the loss, so a person who waits to drink until they are thirsty is already behind, and dehydration is the second leading cause of death in a survival situation.¹⁰ The losses stack fast: a 5 percent loss of body water brings thirst, nausea, and weakness; 10 percent brings dizziness and an inability to walk; 15 percent brings dim vision and can kill.¹¹

• Drink before you are thirsty, in steady amounts through the day — on the order of 6 to 8 quarts a day in hard heat when water allows.¹⁰
• Drink while you eat, since digestion spends water too; if you have food but no water, do not eat until you find water.¹⁰
• Watch your urine: pale and frequent is good, dark and scarce means drink more.¹⁰
• Pace the work. Slow down, rest in shade, and shift the hardest effort to the cooler hours, because sweating can only shed heat about as fast as hard exertion makes it.¹

The Heat-Index Danger

Humidity is what makes heat lethal, and the reason traces straight back to sweat. Cooling depends on sweat evaporating, but when the air is already thick with moisture, the sweat has nowhere to go — it runs off your skin instead of evaporating, and the heat stays in you. The heat index is the single number that folds temperature and humidity together to say what the heat actually does to a body.¹²

The National Weather Service computes it with the Rothfusz regression, where T is air temperature in °F and R is relative humidity in percent:¹²

The NWS sorts the result into four bands of rising danger.¹²

Sources

1. USMC MWTC Summer Survival Course Handbook, ch. 14 (Survival Medicine), heat loss by evaporation (1 qt sweat ≈ 600 calories; max sweating vs. max exertion).
2. USMC MWTC Summer Survival Course Handbook, ch. 14, Heat-Related Illnesses (heat exhaustion mechanism; leads to heat stroke).
3. CDC / NIOSH, Heat-Related Illnesses (heat exhaustion symptoms); corroborated by USMC MWTC Summer Survival Course Handbook, ch. 14.
4. CDC / NIOSH, Heat-Related Illnesses and NOAA / NWS, Heat Cramps, Exhaustion, Stroke (heat exhaustion first aid).
5. USMC MWTC Summer Survival Course Handbook, ch. 14, Heat Stroke (failure of cooling mechanism); core temp >103°F per CDC/NWS.
6. CDC / NIOSH, Heat-Related Illnesses (heat stroke signs and the heat-exhaustion vs. heat-stroke distinction).
7. CDC / NIOSH, Heat-Related Illnesses (heat stroke first aid: 911, rapid cooling, immersion).
8. NOAA / NWS, Heat Cramps, Exhaustion, Stroke (do not give fluids to a victim with altered consciousness).
9. USMC MWTC Summer Survival Course Handbook, ch. 14, Heat syncope and Heat cramps.
10. USMC MWTC Summer Survival Course Handbook, ch. 14, Dehydration and Prevention (second leading cause of death; drink before thirsty; 6–8 qt/day; urine color).
11. USMC MWTC Summer Survival Course Handbook, ch. 14, Dehydration / Water Intake (5%, 10%, 15% body-water loss thresholds).
12. NOAA / NWS Weather Prediction Center, The Heat Index Equation (Rothfusz regression) and NWS Heat Index (equation, risk bands, full-sun caveat).

Cold does not kill you the way a wound does. It works quietly, draining heat faster than your body can make it, until your judgment fails before your body does. The first symptom of serious cold is a person who stops making sense, not a person who complains of being cold. That is why cold injury is a leading killer in a survival situation, and why the work starts long before you feel desperate.¹

Staying Warm: The Layering Principle

Think of how a house keeps heat: not with one thick wall, but with a gap of trapped air inside the wall that the heat cannot cross. Your clothing works the same way. Several light layers trap pockets of still air between them, and that dead air is the insulation. One thick coat cannot do this, and tight clothing crushes the air out and chokes the blood flow that warms your hands and feet.²

The Army packs the rule into one word: COLD. Keep clothing Clean, because matted, dirty fabric loses its trapped air. Avoid Overheating, because sweat soaks your layers and wet clothing stops insulating. Wear it Loose and in layers, so you can add or shed to match your effort. Keep it Dry. When you start to sweat on the move, open your jacket or drop a layer before the sweat soaks in, not after.²

Cover the edges. You lose 40 to 45 percent of your body heat from an unprotected head, and more from a bare neck, wrists, and ankles, because the blood runs close to the surface there. If your feet are cold, put on a hat.²

Hypothermia: When the Core Cools

Hypothermia is the state your body enters when its core temperature falls to 95°F (35°C) or below.¹ It does not take arctic cold to get there. Most cases happen between 30 and 50°F, where wet clothing, wind, and exhaustion pull heat off a person who never thought the day was dangerous.³

Treat hypothermia by stopping the heat loss first. Get the victim out of the wind and off the cold ground, strip any wet clothing, and insulate them completely, including underneath. Rewarm the core before the limbs, skin-to-skin inside a sleeping bag if you have one. Handle the person gently, because a cold heart can be jolted into a fatal rhythm by rough movement, and treat any major bleeding before you rewarm, since warming a body that has bled out does nothing.⁶

Give warm sweet drinks only if the victim is mildly affected and fully alert enough to swallow; otherwise give nothing by mouth. Never give alcohol, which feels warming but dumps heat and clouds judgment. Once you start rewarming, do not stop watching the person.⁶

Frostbite: When Tissue Freezes

Frostbite is the freezing of tissue itself, and it takes the parts farthest from your core first: ears, nose, fingers, toes, cheeks. It announces itself in order. The skin feels cold, then tingles, then goes numb, and the worst sign is when it turns pale and waxy and stiffens so it no longer glides over the joint beneath it.⁷ Current guidance describes the same thing as skin that is white or grayish-yellow, firm or waxy, and numb.⁸

For frosting, rewarm at once with steady skin-to-skin contact: a bare hand over the nose or ear, frostbitten fingers into your own armpit, a buddy's bare belly or armpit for a foot. Hold it for 15 minutes. If the area has not rewarmed in that time, treat it as superficial or deep frostbite and stop trying to thaw it in the field.⁹

Definitive rewarming is done only where refreezing is impossible. The standard is a water bath that is warm, not hot — soak the part in water held at body temperature, not at a heat that would scald skin that cannot feel.¹¹ Field doctrine sets that bath at a strict 101 to 108°F.¹²

The Wind-Chill Danger

Wind does not lower the air temperature, but it lowers you. Moving air strips away the thin shell of warmth your body builds at the skin and keeps stripping it, so a calm 5°F day and a windy 5°F day are not the same threat to bare skin. Wind chill is the number that expresses how fast that heat leaves, and it endangers the person who is not properly dressed for it.¹³

The National Weather Service calculates it with this formula, where T is air temperature in °F and V is wind speed in mph:¹⁴

The number matters because it tells you how fast exposed skin freezes. The NWS chart marks three frostbite bands by the wind-chill value, and they collapse fast as it drops.¹⁴

Sources

1. USMC MWTC Winter Survival Course Handbook, ch. 14 (Survival Medicine), Cold Weather Injuries — Hypothermia.
2. US Army Survival Manual (FM 21-76, 2006) — Basic Principles of Cold Weather Survival (the COLD principle; head/neck heat loss).
3. USMC MWTC Winter Survival Course Handbook, ch. 14, Hypothermia (temperature range of most cases).
4. USMC MWTC Winter Survival Course Handbook, ch. 14, Signs and Symptoms of Hypothermia (altered mental status; shivering ceases ~90°F).
5. USMC MWTC Winter Survival Course Handbook, ch. 14 ("not dead until you are warm and dead").
6. USMC MWTC Winter Survival Course Handbook, ch. 14, Treatment of Hypothermia and Other Points to Remember.
7. USMC MWTC Winter Survival Course Handbook, ch. 14, Frostbite (definition and degrees).
8. NOAA / National Weather Service, During Cold — Frostbite & Hypothermia (frostbite signs and first aid).
9. USMC MWTC Winter Survival Course Handbook, ch. 14, Treatment of Frostbite (15-minute rewarm rule).
10. USMC MWTC Winter Survival Course Handbook, ch. 14, Treatment of Superficial or Deep Frostbite (freeze-thaw-refreeze; do not rub or use fire).
11. NOAA / National Weather Service, During Cold — Frostbite & Hypothermia (do not rub; warm not hot water; do not break blisters; emergency care).
12. USMC MWTC Winter Survival Course Handbook, ch. 14 (definitive rewarm water bath, 101–108°F).
13. USMC MWTC Winter Survival Course Handbook, ch. 14, Causes of Hypothermia (wind chill affects improperly clothed individuals).
14. NOAA / National Weather Service, Wind Chill Chart (2001 wind chill formula and frostbite-time bands; effective 11/01/01).

A dog hears a knock at the door a second before you do. The pressure of an approaching storm reaches you the same way, ahead of the cloud, in signs you can read off the sky and the wind. None of this needs a barometer. The rules below work because the weather of the mid-latitudes moves on a pattern, and the pattern leaks.

Pressure is the headline

Falling air pressure means a low-pressure system is moving in, and lows carry the wind, cloud, and rain.² Rising or steady high pressure means descending air that smothers cloud and storm, so calm and clear skies usually signal a high in charge.¹

The speed of the fall matters more than the number. The National Weather Service calls pressure "falling rapidly" at a drop of 0.06 inch of mercury or more in one hour.³ A fall of about four millibars over three hours runs ahead of most storms, and a drop near ten millibars in eight hours points to a gale.² If you carry any barometer, watch the trend, not the reading.

Read the wind

Stand with your back to the surface wind and look up at the high clouds. If those upper clouds cross from your left, a low is arriving and the weather will worsen. If they cross from your right, the low has passed and the weather will improve. This is the crossed-winds rule, and it reverses in the Southern Hemisphere.¹

A wind that swings counterclockwise, from west around toward south and then east, is the front edge of a low closing on you, often gusty and wet. A wind that settles into the steady west is the back of the system leaving, and the fair weather behind it tends to hold.¹

The sky at sunrise and sunset

"Red sky at night, sailor's delight; red sky in morning, sailor's warning" survives because it describes real physics. A red sky is sunlight scattered through dry, dust-laden air sitting under high pressure. With systems moving west to east, an evening red sky means that dry high pressure lies to your west and is heading your way. A morning red sky in the east means the high has already passed and a low is following behind it.¹

A ring around the sun or moon is light bent through ice crystals in high, thin cloud. That high cloud is often the leading edge of an approaching system, so a halo warns of a change in the next eighteen to thirty-six hours.¹ In deep winter, though, a halo can simply mean very cold, clear air, so weigh it against the wind and the pressure.

Lesser signs that hold up

• Sound carrying far and sharp in summer means moist air is moving in, and moist air runs ahead of bad weather. In cold, dry winter the rule weakens, because cold air also carries sound well.¹
• Doors swelling and salt clumping mean the air is heavy with moisture, which raises the chance of rain.¹
• Old joint aches that flare can track a falling pressure that lets irritated tissue swell, though the evidence is mixed and easy to read into.¹

• Note the wind direction now, and check it again in an hour for a swing.
• Look up: are the high clouds crossing left (worse) or right (better)?
• Watch the pressure trend if you have a barometer; a fast fall outranks the number.
• Read the dawn or dusk sky color and place it west-to-east.
• Treat a sudden calm under building western cloud as a warning, not a break.

Sources

1. Weather Lore (2017) — sayings with observational validity: red sky, halo, crossed-winds, low-pressure wind shifts, calm conditions, sound transmission, humidity and aches.
2. NOAA JetStream — Air Pressure; falling pressure and storm association, rate-of-fall rules of thumb.
3. NWS Glossary — Pressure Falling Rapidly (0.06 inHg or more per hour).

Merrill's Marauders fought their way across Burma and were taken off the line not by the enemy but by dysentery; one platoon cut the seats out of their trousers because the diarrhea would not wait for a lull in the fighting.¹ That is the real shape of a long deployment. Across every war the United States has fought, four out of five hospital admissions came from disease and non-battle injury, not from combat.¹ In the field, sanitation is not housekeeping. It is the side of the fight that quietly removes more people than bullets do.

Wash your hands

Handwashing with soap is the single cheapest defense you have against the disease that empties a camp. It prevents roughly thirty percent of diarrhea-related illness, and disciplined community handwashing cuts that illness by twenty-three to forty percent.² Soap and water lift germs that hand sanitizer cannot kill, including norovirus and the parasite that causes cryptosporidiosis.²

• Wash after using the latrine and before touching food, every time, with no exception.
• Use soap and the friction of scrubbing, then rinse; the mechanical action does the work.²
• Set up a handwashing point at the latrine and at the cooking area, and make its use mandatory.³

Discipline human waste

Flies walk on feces and then on your food, and that short trip is how a camp poisons itself. Site human waste so it can never reach what you eat or drink.

• On the move, use a sealed personal waste bag; a cat-hole is the fallback only when the unit is moving.³
• In a settled camp, dig and cover a latrine, clean it daily, and bury or burn waste daily.³
• Never dig a latrine uphill of your water source.

Food and water discipline

Treat every wild water source as contaminated until you have made it safe. Disinfect with iodine tablets or chlorination, and if you treat bulk water, check that a chlorine residual is still present before anyone drinks.³

• Refill containers only with treated water.³
• Keep food covered and off the ground so flies and rodents cannot reach it.³
• Do not eat in sleeping areas; scraps draw insects and animals into where you rest.³

Skin and foot care

Skin that stays wet, dirty, and warm grows the infections that take a person off their feet. Wash daily with a cloth and soapy water even when a shower is out of reach, paying attention to the feet, armpits, groin, and any skin that stays damp.³ If water is too scarce even for that, strip down and air-bathe in sun and wind for about an hour, watching for sunburn.⁴

• Wear loose cotton next to the skin, never nylon or silk, so sweat can dry.³
• Powder the feet and any chafing area to keep them dry.³
• Bathe and change into clean clothing about once a week to keep body lice down.³

Sources

1. Field Hygiene and Sanitation (FM 21-10 / MCRP 4-11.1D, 2000) — disease and non-battle injury share, Merrill's Marauders, skin and foot care, lice control, trench foot temperatures.
2. CDC — Handwashing Facts: ~30% reduction in diarrheal illness; 23–40% from community promotion; soap vs. norovirus and Cryptosporidium.
3. Field Hygiene and Sanitation (FM 21-10 / MCRP 4-11.1D, 2000), Ch. 3 — latrine and food-waste distances, water disinfection and chlorine residual, mandatory handwashing points.
4. US Army Survival Manual (FM 21-76, 2006) — personal hygiene in a survival situation; the air bath.

Picture the kitchen jar where loose change lands. Coins go in all month, you grab a handful when you need bus fare, and at any moment the jar holds whatever the two flows leave behind. A battery in an outage is that jar. Power flows in from a panel or a generator, your fridge and lights pull it back out, and what is left is your runtime. So you start by counting the coins you spend.

Count your watt-hours first

Every device draws a number of watts while it runs, and a watt-hour is one watt drawn for one hour. Multiply each device's watts by the hours you run it in a day, then add the devices together, and you have your daily load in watt-hours.¹ A watt is just amps times volts, so a label that reads 0.3 amps at 120 volts is a 36-watt load.¹ This one number drives every sizing decision that follows; skip it and you are buying a battery blind.

What the battery actually holds

A battery's rated capacity and its usable capacity are two different numbers, and the gap is where people run out of power early. Capacity is rated in amp-hours at a voltage, or directly in watt-hours; amp-hours times volts gives watt-hours, so a 50 amp-hour 12-volt battery is rated at 600 watt-hours.¹ But you never get all of it. Draining a battery to empty wrecks it, so each chemistry has a floor you stop at, and only the part above that floor is yours to spend.

Lead-acid is the cautious one. Discharge it past about half and you cut its life hard, so you plan on roughly 50 percent of the rated capacity as usable.^1,2 Lithium iron phosphate, the LiFePO4 chemistry in most modern power stations, takes a far deeper draw — 80 percent is the safe planning figure, and the cells tolerate close to 100 percent in a pinch.² The practical result is blunt: a LiFePO4 battery delivers the same usable energy as a lead-acid battery rated nearly twice its size.²

The runtime math

Now you divide. Usable watt-hours divided by your load in watts gives hours of runtime. The old extension-service example runs it cleanly: a 50 amp-hour battery at 50 percent usable is 25 amp-hours, times 12 volts is 300 usable watt-hours, divided by a 36-watt load gives 8.3 hours of power.¹ Swap in your own load total and you have your real number.

Sizing a bank for a multi-day outage flips the same math around. Take your daily watt-hours, multiply by the days you want to last, divide by the chemistry's depth of discharge, then divide again by inverter and wiring efficiency of about 0.85.³ A 1490 watt-hour day for three days on LiFePO4 works out to 1490 × 3 ÷ 0.80 ÷ 0.85, roughly 6,600 watt-hours of rated battery — the gap between that and the bare 4,470 you spend is the cushion the chemistry and the wiring take off the top.

Charging back from the sun

A battery only buys time; solar refills the jar. To size a panel array, you ask how many watt-hours you burn in a day and how many hours of full-strength sun your location gives — the peak sun hours, the equivalent hours of bright midday sun, which is well under the hours of daylight.⁴ Then you account for losses, because panels never deliver their nameplate watts: heat, dirt, wiring, and inverter waste eat 25 to 30 percent.⁴

The formula is panel watts equals daily load watt-hours divided by peak sun hours, divided by a loss factor of about 0.7.⁴ A 1490 watt-hour day at four peak sun hours needs 1490 ÷ 4 ÷ 0.7, about 530 watts of panel just to break even on a good day — and a cloudy week is why the battery bank, not the panel, carries you through.^3,4

Sources

1. When the Power Goes Out (Coping with Power Failures), Oregon State University Extension Service, EM 8734 — watts/amps/volts identity, the storage-battery capacity worked example (50 Ah × 50% × 12 V = 300 Wh ÷ 36 W = 8.3 h), the 50% lead-acid discharge limit, and the 3× motor start-up surge.
2. RELiON, Depth of Discharge, State of Charge, and the Effect on Capacity, and Anern, LiFePO4 vs. Lead-Acid Sizing — usable depth of discharge ~50% lead-acid, ~80–100% LiFePO4.
3. TheGreenWatt, Solar Battery Bank Sizing, and Unbound Solar, Battery Bank Sizing — (daily Wh × days of autonomy) ÷ DoD ÷ system efficiency.
4. Anern, The Definitive Roadmap to Sizing Your Power System, and EleCalculator, Solar System Sizing Chart — panel watts = daily load Wh ÷ (peak sun hours × ~0.7 loss factor); peak sun hours; 25–30% system losses.

Think about how you dress to leave the house in winter. Keys and phone go in your pockets and never leave you; a coat goes on for the cold; a packed bag rides in the car for the long trip. Each layer covers a wider problem than the one inside it, and you are never caught with nothing. A readiness kit works the same way: a small kit on your body, a larger one you can grab, and a deep store at home, each carrying you through a longer stretch of trouble.

The layers

The innermost layer is what you carry at all times — a few tools and a light chosen for the most likely scenario, contained in the clothes you already wear.¹ The next ring out is the bag you can grab on the way through the door; from there the kits get larger and more specialized through your car and your home.¹ The point of the rings is that a disaster never asks whether you had time to pack.

Cutting the layers a second way, by time, gives you the planning targets most people use. A 72-hour kit covers the first three days, the window FEMA builds its basic list around; a three-week store is for staying put through a longer outage; three months and beyond is long-term resilience.² The community shorthand maps onto these: an every-day-carry bag for daily life, a get-home bag in the car or at work for about a day on foot, and the bug-out bag, which is the portable 72-hour kit itself.²

The core: FEMA's basic kit

FEMA's recommendation has held steady for years, and water leads it: one gallon of water per person per day for at least three days, for drinking and sanitation.³ Food is next — at least a three-day supply of non-perishable food.³ The rest of the basic list is the gear that lets you hear, see, signal, and stay put when the grid and the water main quit.^3,4 Build this first; everything else is tailoring.

• Water — one gallon per person per day, at least three days, for drinking and sanitation
• Food — at least a three-day supply of non-perishable food
• Battery-powered or hand-crank radio, and a NOAA Weather Radio with tone alert
• Flashlight and extra batteries
• First aid kit
• Whistle to signal for help
• Dust mask, plus plastic sheeting and duct tape to shelter in place
• Moist towelettes, garbage bags, and plastic ties for personal sanitation
• Wrench or pliers to turn off utilities
• Manual can opener (if the kit holds canned food)
• Local maps
• Cell phone with chargers and a backup battery

Past the core sit the items that turn survival into function: prescription medication and spare glasses, infant formula and diapers, pet food and water, cash in small bills, and copies of insurance, identification, and bank records sealed in a waterproof container.⁵ Pack a sleeping bag or warm blanket and a full change of clothing per person, a fire extinguisher, and matches in a waterproof container.⁵

Tailor it to you

The list is a floor, not a finished kit. FEMA tells you plainly to review it against where you live and what your family needs, and to keep a full kit at home plus smaller kits in your vehicle and workplace.^3,4 A cold climate adds bedding and clothing; a flood plain changes your maps and your exit routes; a member who depends on a medication or a device changes the whole calculus.^1,5 The kit that fits your real hazards beats the bigger generic one every time.

Sources

1. Urban Preparation Kit, Part I — On-Body Kit (Schwert, Outdoors-Magazine.com, 2004) — the concentric-ring layering concept and the local-conditions tailoring of a kit.
2. Practical Emergency Preparedness — Recommended Steps to Developing Your Own Plan (slide deck) — progressive 72-hour / 3-week / 3-month timeframes and the EDC / GHB / BOB definitions.
3. FEMA / Ready — Build A Kit — water one gallon per person per day for at least three days, three-day non-perishable food supply, the basic item list, and the instruction to review and adapt the kit and keep kits at home, work, and in the vehicle.
4. 72-Hour Emergency Supply Kit Checklist (FEMA Ready Emergency Supply List) — the verbatim basic-kit water and food lines and the full recommended item list.
5. 72-Hour Emergency Supply Kit Checklist, additional-items page — prescriptions and glasses, infant and pet needs, waterproofed documents, cash, bedding, clothing, fire extinguisher, matches, and the bleach water-treatment ratio (16 drops unscented bleach per gallon).