How much water is needed for 72 hours?

January 6, 2026 •

4 min read

According to the U.S. Federal Emergency Management Agency (FEMA), the standard recommendation is one gallon of water per person per day for a minimum of three days. This critical supply covers both drinking and basic sanitation needs during an emergency when clean water may be unavailable.

Quick Summary

This guide outlines the water requirements for a 72-hour emergency kit, including how to calculate needs based on individual factors, proper storage methods, and purification techniques for safety. The information details guidelines for drinking and sanitation, plus alternative water sources if supplies run low.

Key Points

Minimum Standard: Stock at least one gallon of water per person per day for a 72-hour period.
Personalize Needs: Adjust the standard amount for factors like climate, age, activity level, and special health requirements.
Account for All Uses: The recommended amount includes water for drinking, cooking, and basic personal hygiene.
Use Safe Containers: Only store water in FDA-approved food-grade containers, avoiding previously used milk or chemical jugs.
Master Purification Methods: Learn how to boil, disinfect with bleach, or use a portable filter to make additional water safe if needed.
Rotate Your Supply: Replace your stored water every six months for home-filled containers to ensure freshness and safety.
Consider Pet Needs: Don't forget to include extra water for pets, as they may also require more when under stress.

Calculating Your 72-Hour Water Needs

While the one-gallon-per-person-per-day rule is a solid baseline, several factors can increase your water requirements. These variables include climate, age, physical activity level, and special health conditions. For instance, individuals in hot climates or those performing strenuous labor will need more water to prevent dehydration. Similarly, children, nursing mothers, and people who are sick require additional fluids. Your total need includes water for drinking, cooking, and basic hygiene.

Determining Individual Water Consumption

To get a more personalized estimate for drinking water needs over 72 hours, consider the following calculation:

General Rule: Multiply the standard daily recommendation (1 gallon or approximately 3.78 liters) by three days. For a single person, this totals 3 gallons for drinking and sanitation.
Body Weight Method: A personalized formula suggests drinking 2/3 of your body weight in pounds, converted to ounces, daily. For example, a 180-pound person would need approximately 120 ounces (nearly 1 gallon) per day. For 72 hours, this is 360 ounces or roughly 2.8 gallons. Add more for high activity or heat.
Activity Adjustment: Add an extra 12 ounces of water for every 30 minutes of strenuous activity. If you anticipate high physical exertion during an emergency, factor this into your total.

Water Storage: Containers and Rotation

Proper water storage is essential for maintaining a safe and clean supply. Choosing the right container and rotating your supply are key steps in emergency preparedness. The Centers for Disease Control and Prevention (CDC) recommends using food-grade containers that are durable and have a tight-fitting lid. Avoid containers previously used for toxic substances or milk, as milk protein is difficult to remove and promotes bacterial growth.

Water Storage Options

Commercial Bottled Water: Purchased bottled water is the safest and most convenient option, with a shelf life of up to five years if stored properly.
DIY Filled Containers: Food-grade plastic containers (found at outdoor supply stores) are a reusable option. Fill these with tap water and add unscented household bleach (8 drops per gallon) if your water is not already chlorinated. Label and date the containers clearly.
Large Water Barrels: For families or long-term storage, 55-gallon or larger food-grade barrels are a reliable option, though they are heavy and require a pump or siphon for access.

To ensure freshness, rotate your water supply. Water stored in DIY containers should be replaced every six months, while commercially bottled water can last longer. Store all water in a cool, dark place away from chemicals, fuel, and direct sunlight.

Emergency Water Purification Methods

Even with a stored supply, it is vital to know how to purify water from other sources in case reserves run out or become contaminated. The U.S. Environmental Protection Agency (EPA) provides guidance on effective purification techniques.

Comparison of Water Purification Methods


Method	Effectiveness Against Pathogens	Considerations
Boiling	Kills all bacteria, viruses, and parasites.	Requires a heat source and takes time to cool. Does not remove chemical pollutants.
Chemical Disinfection (Bleach)	Kills most viruses and bacteria, but less effective against Cryptosporidium.	Requires fresh, unscented household bleach. Follow instructions carefully and wait 30 minutes for disinfection.
Water Filters	Most portable filters remove bacteria and protozoa, but not viruses. Advanced models may filter viruses.	Requires no heat source. Check manufacturer's specifications on what is removed.
UV Light	Kills most viruses and bacteria, but less effective in cloudy water.	Requires batteries for portable units. Water must be pre-filtered if cloudy.

Conclusion

Preparing a 72-hour water supply is a fundamental part of any emergency plan. A baseline of one gallon per person per day is the widely accepted standard, covering basic drinking and sanitation needs. By factoring in individual circumstances like climate, activity level, and health, you can adjust this quantity to meet your family's specific needs. Proper storage in food-grade containers, regular rotation, and knowledge of emergency purification methods provide the confidence and resilience to face unforeseen disruptions with adequate water resources. Being prepared today ensures a safer tomorrow for you and your loved ones.

How Much Water is Needed for 72 Hours?

Standard Recommendation: Store at least one gallon of water per person per day for drinking, cooking, and sanitation over a 72-hour (3-day) period.
Higher Needs: Increase your stored water amount if you live in a hot climate, are pregnant, nursing, or have a family member who is sick.
Sanitation Included: The 'one gallon per person' recommendation already factors in basic hygiene, so you don't need a separate calculation for this.
Proper Storage: Use food-grade containers and store them in a cool, dark place, away from sunlight and chemicals, to prevent contamination.
Regular Rotation: For home-filled containers, rotate the water every six months. Commercially sealed bottled water can be stored longer.

Frequently Asked Questions

The Federal Emergency Management Agency (FEMA) recommends storing a minimum of one gallon of water per person per day for at least three days.

Yes, individuals in hot climates will need to increase their stored water supply to account for higher fluid loss through sweating.

Use FDA-approved, food-grade plastic containers. Avoid using containers that previously held toxic chemicals, milk, or other porous materials.

If you fill your own containers with tap water, you should replace the supply every six months. Commercially bottled water, if stored in a cool, dark place, can last up to five years.

No, the general recommendation does not include pets. You should plan for additional water for any animals in your household, with one gallon per pet per day as a good guideline.

If your stored water runs out, you can access alternative sources such as your hot water heater tank or toilet tank (if no chemical cleaners are used). Any water from these alternative sources must be purified before drinking.

No, while boiling is the most effective method for killing pathogens, you can also use chemical disinfection with unscented bleach, portable water filters, or UV light purifiers. Each method has different considerations.

Storing water in a cool, dark place prevents algae growth and slows the degradation of plastic containers. Keeping it away from chemicals ensures fumes do not contaminate the water.