Water Basics For Preparation and Survival

Bob Mayer
5 min readMar 2, 2023



For most emergencies and disasters, water will end up being your number one priority. Ever notice that one of the first things brought in after a disaster is pallet loads of bottled water? Be prepared ahead of time!

On average, we can survive three days without water versus three weeks without food.

Over three-quarters of your body is composed of fluid. Perspiration is not the only way you lose water. We actually lose more water just by breathing. And you can’t stop that loss. We lose around 2 to 4 cups of water a day by exhaling (16 cups equal one gallon). We lose about 2 cups via perspiration. We lose ½ to a cup just from the soles of our feet. We lose six cups via urination. When you add that up (and it wasn’t easy converting all that) you lose more than half a gallon of water a day just existing; more depending on the weather and your activity level.

Water is critical for functioning. A 5% drop in body fluid will cause a 25% drop in energy level. A 15% drop will cause death. Even in normal day-to-day living, it is estimated that 80% of people are fatigued simply because they are chronically dehydrated.

In your home, you need to be prepared for at least 3 days for mild emergencies, but I recommend doubling that. Your average water bottle is 500 milliliter. Here’s the math to make it easy: 7.5 bottles equal a gallon. Your average case of water has 24 bottles, so let’s round up to three gallons. That will last a person 3 days. A case of water per person in the household will last three days. If you are in a very hot environment, definitely double that.

Regardless, I recommend storing at the very least two cases of water per person in the household. The FDA considers bottled water to have no expiration date as long as the lid is sealed. Expiration dates printed on bottles are voluntary and reflect concern over taste and color; not safety.

Depending on the possibilities of emergencies in your area, more is better. FEMA recommends having at least a two-week supply for moderate emergencies. I recommend a month at a gallon per person, per day for extreme emergencies.

This is your number one priority: Get the water if you haven’t already!

Stop procrastinating.

In your home, you can add another half-gallon of water per person for things such as cleaning, brushing teeth, etc. This isn’t essential, but useful for mild situations. Do not use drinking water for these reasons if you’re in a moderate or extreme emergency.

Your water in your house is ultimately dependent on electricity. While you may have had running water during the last local blackout, a major blackout will shut down the water processing and pumping stations. If you have a well, the pump runs off electricity. Can you get water out of your well without power?

Do you have pets? Add in water for them, but in moderate or extreme emergencies, let them forage for water. They can do it much better than you.

Quite a bit of the food you have stored will require water to prepare. That’s why you might think the recommended gallon a day seems high.

We have water already stored in houses in places we might not automatically think of:

Our hot water heater contains a considerable amount. There is a drain at the bottom. Make sure you have something to collect the water in, open the drain, then open a faucet to complete the water circuit. (Make sure, if not already off, that you turn off the gas/power to the heater before working on it. If the power/gas is already off and comes on, make sure you immediately refill the heater before turning it back on or else it can overheat.)

The water pipes in your house can be drained of the water in them.

Our toilet tank (not the toilet bowl) contains fresh water. Get over it and use it.

A swimming pool or hot tub contains non-potable water which you can make potable. These techniques are covered in Survival.

If you have adequate warning, you should fill every available container with potable water. Also fill all tubs and sinks.

Mod/Ex: Long term storage of a large supply of water:

Using milk containers or other thin plastic is not recommended for storing water as thin plastic degrades and will leak. You can use soda or juice bottles with thicker plastic. Glass is fine, except it is heavy and subject to breakage.

To re-use such containers, thoroughly clean them out with soap and water, then rinse completely, insuring there is no residual soap.

Sanitize these bottles by adding one teaspoon of un-scented chlorine bleach to every quart (note that bleach also has a shelf-life of six months, so make sure it is fresh). Shake the container, with the lid on, thoroughly sanitizing it. Empty, wash out with clean water. Then fill it and add two drops non-scented bleach and tightly seal the top.

Date the outside of the container with a permanent marker.

Store in a dry, cool place.

Rotate every six months.

If you’re going with smaller sized containers like this, stagger filling them so that they all don’t come due to be refilled at the same time which, according to Murphy’s Law, is usually about the time you’ll need the water. However, if necessary, consider this water potable in an emergency if it is your only option. The rotation is to err on the side of caution.


What can screw up.


There are larger size water containers for sale. There are fixed sided containers and collapsible bladders. If you want to store large quantities of potable water, 55 gallon drums work well. Make sure they are food grade (HDPE #2).

Check stored water every two months and refill at a minimum of every six months. Remember, once you fill this barrel, you won’t be able to move it because water is heavy. This is also something to factor in when considering how much water you can carry.

Water weighs 8.34 pounds per gallon. (3.78 Kg)

You should carry water in your car. Store a case of water somewhere inside your vehicle for Mod/Ex. For Mild have two bottles within arm’s reach of the driver’s seat in case you are trapped.

Learn your local area (we’ll cover this in detail in the Area Study). Do you have a natural source of drinkable water within walking distance? Is there one near your BOHS? Once more, you must consider any water in nature to be contaminated.

There are items that can be used to purify water and some of these will become part of your Grab-n-Go bags. These are:

Survival straw

Survival filter

Water purification tablets

Suggestions and links to these items are at the end of the book in the Appendix Gear.

Field expedient means for disinfecting water are covered under survival.

This is just a partial excerpt from The Green Beret Preparation and Survival Guide

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Bob Mayer

West Point grad; Special Ops Vet; NY Times bestseller of over 80 books; for free books and over 200 free downloadable slideshows go to www.bobmayer.com