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Storing 100 gallons of water at home

By the Plain Prepper editors. Updated 2026-10-14.

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Quick answer

One hundred gallons is about 25 days of drinking and sanitation water for a family of four at Ready.gov's one gallon per person per day. A vertical potable tank holds it in a small footprint. Norwesco's 100 gallon water tank is 23 inches across and 63 inches tall, made from FDA-approved resin in black or green to limit algae. A WaterBOB bathtub bladder holds up to 100 gallons, but you fill it as a storm approaches and it keeps water fresh for up to 16 weeks.

What 100 gallons covers

Ready.gov says to store at least one gallon per person per day for drinking and sanitation, and notes that very hot weather can double the need. At that rate, 100 gallons lasts:

People	Days at 1 gal/person/day
1	100
2	50
4	25
6	About 16

FEMA suggests at least a two-week supply per person, so a family of four meets that with room to spare. A family of six falls just past two weeks.

Option 1: a slim vertical tank

Norwesco's catalog lists a 100 gallon above ground water-only tank at 23 inches in diameter and 63 inches tall, in black (part 41464) or green (41465). For comparison, its 120 gallon tank is a squat 38 by 31 inches. A tall, narrow 100 gallon tank fits a utility-room or garage corner that a wide tank cannot.

• Norwesco says its water tanks use resins with FDA approval for potable water and carry NSF61 approval where applicable.
• The black or green color limits light, which reduces algae growth.
• Each water tank comes with an overflow fitting near the top, plus outlet fittings.
• The tanks are rated for water only, never chemicals or fertilizer.

Option 2: a bathtub bladder before the storm

The WaterBOB is a 10 mil food-grade LLDPE liner that sits in a bathtub. Its maker says it holds up to 100 gallons, fills from the tub faucet in about 20 to 30 minutes, and comes with a siphon pump to fill jugs and pitchers. It also notes that most standard tubs hold about 60 to 70 gallons, and not to fill it over the tub's edge, so your real capacity depends on your tub.

It is a short-term tool. The maker says water stays fresh for up to 16 weeks depending on humidity and temperature, while the same FAQ later refers to a 4 week safe storage time. Plan on the shorter figure. It is designed for one-time use, so it is for hurricanes and forecast storms when you have warning, not year-round storage. Cover it with towels or a sheet to keep sunlight off.

Option 3: smaller containers that add up

FEMA recommends food-grade water storage containers and says not to reuse milk or juice jugs, since milk protein and fruit sugars cannot be fully removed. Twenty 5 gallon containers make 100 gallons and can be moved one at a time, which helps in apartments or if you may need to leave home. The trade-off is more lids to check and more containers to refill every six months.

The three compared

	Vertical tank	Bathtub bladder	Containers
Holds	100 gal	Up to 100 gal, often 60 to 70 by tub size	As many as you buy
Storage time	Refresh every 6 months (FEMA)	Up to 16 weeks, or 4 by the FAQ's other figure	Refresh every 6 months (FEMA)
Footprint	23 in circle, 63 in tall	Your bathtub	Stacks or shelves
Portable	No, once full	No	Yes, per container
Reusable	Yes	One-time use	Yes

Filling and keeping it safe

A 100 gallon reserve is only as good as the water in it. Wash and sanitize the tank or each container before the first fill. City water that is already chlorinated goes in as is, per FEMA. Well water gets two drops of unscented household bleach per gallon, which is about 200 drops, or roughly 2.5 teaspoons, for the whole tank. WaterBOB also tells well-water users to treat its bladder right after filling.

Write the date on the tank, keep it out of the sun, and swap the water every six months, as FEMA and Ready.gov advise. If you ever doubt it, Ready.gov's fix is 1/8 teaspoon of regular unscented bleach per gallon, stirred, then 30 minutes of standing time.

What to look for when you buy

Questions people ask

How long will 100 gallons of water last?

At Ready.gov's one gallon per person per day, about 25 days for a family of four, or 50 days for two people.

How big is a 100 gallon water tank?

Norwesco's 100 gallon water tank is 23 inches in diameter and 63 inches tall.

How long does water stay fresh in a WaterBOB?

Its maker says up to 16 weeks depending on humidity and temperature, though the same FAQ also mentions a 4 week safe storage time. Use the shorter figure.

How often should I change stored water?

FEMA and Ready.gov say to replace water you store yourself every six months.

Sources

• Liquid Storage Tanks Catalog 2024 (above ground water tanks), Norwesco
• Order waterBOB (description and FAQ), waterBOB
• Water, Ready.gov
• Food and Water in an Emergency, FEMA and American Red Cross

Sources checked 2026-10-14.