How Much Emergency Water Does Your Family Need?

The baseline: 1 gallon per person per day

The CDC recommends storing at least 1 gallon of water per person per day for at least 3 days, and a 2-week supply if possible. Ready.gov uses the same 1-gallon figure and specifies that it covers drinking and sanitation.

Plan for more in some situations. The CDC suggests storing extra for pregnant women, people who are sick, pets, and anyone living in a hot climate. Ready.gov adds that children, nursing mothers and sick people may need more, a medical emergency might require additional water, and in very hot temperatures water needs can double.

Worked example: how many gallons to store

Multiply people by days by 1 gallon. The figures below are the CDC baseline; add a margin for pets, hot weather, illness or pregnancy. The hot-weather column applies Ready.gov's note that needs can double in very hot temperatures.

• 1 person: 3 days = 3 gal | 14 days = 14 gal | 30 days = 30 gal | 14 days in extreme heat = up to 28 gal
• 2 people: 3 days = 6 gal | 14 days = 28 gal | 30 days = 60 gal | 14 days in extreme heat = up to 56 gal
• 4 people: 3 days = 12 gal | 14 days = 56 gal | 30 days = 120 gal | 14 days in extreme heat = up to 112 gal
• 6 people: 3 days = 18 gal | 14 days = 84 gal | 30 days = 180 gal | 14 days in extreme heat = up to 168 gal
• Pets: the CDC recommends extra water for pets but does not give a fixed amount; ask your veterinarian.

Storing water safely

Ready.gov recommends buying commercially bottled water and keeping it sealed in its original container in a cool, dark place. For water you bottle yourself, the CDC recommends food-grade containers with tight-closing lids, ideally with a narrow neck for pouring, and advises against glass and against containers that ever held toxic substances such as bleach or pesticides.

• Clean containers with soap, then sanitize with 1 teaspoon of unscented bleach per quart of water before filling (CDC, Ready.gov).
• Store between 50°F and 70°F, out of direct sunlight, away from gasoline and pesticides (CDC).
• Replace self-stored water every 6 months; follow the expiration date on store-bought water (CDC, Ready.gov).
• Use a clean scoop and never dip hands into stored water (CDC).
• Never ration drinking water unless authorities tell you to; drink what you need today and look for more tomorrow (Ready.gov).

Backup sources inside your home

The CDC lists several emergency sources already inside most homes: water from the water heater tank that supplies your faucets (not a separate tank that heats radiators), ice made from uncontaminated water, clear toilet tank water (not the bowl) that has not been treated with colored cleaners, and liquid from canned fruits and vegetables. Pool and spa water is for hygiene and cleaning only, not drinking (CDC).

Can I use lake or river water in an emergency?

Only after treatment, and not always. The CDC warns that rivers, streams and lakes can be contaminated with livestock waste, sewage, chemicals and other pollutants, and that water from outside sources must be treated to kill germs. The CDC lists rainwater, moving water, ponds, lakes and natural springs as sources that can be made safe by treatment.

There are two important exceptions. First, the CDC says not to use water contaminated by fuel or toxic chemicals at all, because it cannot be made safe. Second, if a lake or pond has a harmful algal bloom, the CDC states that boiling water containing toxins will not make it safe to drink, and that boiling can concentrate the toxin. Follow local officials' guidance on blooms and use a different source.

Treating water: boiling, bleach and their limits

Let cloudy water settle or filter it through a clean cloth, paper towel or coffee filter first (CDC, EPA). Then:

• Boil: bring clear water to a rolling boil for 1 minute. The CDC says 3 minutes above 6,500 feet; the EPA says 3 minutes above 5,000 feet. Using the longer time at any high elevation covers both.
• Bleach: use only unscented bleach labeled for disinfection. EPA: 8 drops per gallon for 6% bleach, 6 drops per gallon for 8.25% bleach. The CDC gives 8 drops per gallon for bleach between 5% and 9%. Double the dose for cloudy, colored or very cold water, stir, and wait 30 minutes (CDC, EPA). Follow the bleach label's directions first if it has them (CDC).
• What boiling and bleach do not do: the EPA says boiling or disinfection will not destroy heavy metals, salts and most other chemicals. Ready.gov's comparison shows that boiling and chlorination kill microbes but do not remove other contaminants; distillation does both.
• Cyanotoxins: boiling does not remove algal toxins and can concentrate them (CDC).

What about countertop and portable filters?

Filters are useful, but they are not a complete solution on their own. The CDC says portable filters do not remove all types of germs. A filter with an absolute pore size of 1 micron or smaller, or one certified to NSF Standard 53 or 58 for cyst reduction, removes parasites; a pore size of 0.3 micron or smaller is needed for bacteria; and most filters do not remove viruses, with reverse osmosis being the exception the CDC names.

That applies to gravity-fed countertop systems, including Berkey-type units, as much as to camping filters. Check exactly which independent certifications a specific model holds rather than relying on marketing claims, and follow the CDC's advice to disinfect water after filtering to handle viruses and bacteria. Do not assume any filter makes fuel- or chemical-contaminated water safe; the CDC's guidance is to use another source.