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Poly water tanks: pick the shape, the grade and the spot

By the Plain Prepper editors. Updated 2026-10-15.

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Quick answer

Poly water tanks are molded from polyethylene in shapes for different jobs: vertical tanks for fixed storage, horizontal leg tanks and pickup tanks for hauling, and low-profile tanks for trailers. Norwesco's water-grade tanks are rated for liquids up to 9.2 pounds per gallon, so they are for water only, and its black or dark green tanks block light to slow algae. Keep contents under 120°F, never bury an above-ground tank, and follow CDC rules: food-grade containers, labeled, out of sunlight and refreshed every 6 months.

Four tank shapes and what each is for

Shape	Typical use	Norwesco example sizes	Notable features
Vertical (black or dark green)	Fixed storage beside a house, barn or cabin	120 to 550 gal and up; 165 gal is 31 in wide by 56 in tall	Dark color limits light and algae; water only
Horizontal leg	Hauling in a truck bed or trailer; low stationary storage	35 to 525 gal; 125 gal is 32 in diameter by 41 in long	Gallon markings, slosh-proof lid, bulkhead fitting standard
Pickup truck	Fits the bed of a pickup	210, 305, 325, 425 gal	Low profile for rear vision; fill opening offset to the side
Low profile and box	Trailers and large trucks	1,250 to 2,400 gal	Slosh-reduction ribs; can also sit stationary

Norwesco notes that its 525 gallon horizontal leg tank needs full-length support, and that tank dimensions may vary slightly. Choose a leg or pickup tank only if you also need to haul water from a refill point.

Grade and color matter

Norwesco builds above-ground tanks in two grades:

• Water grade: rated for a specific gravity up to 1.1, which is 9.2 pounds per gallon at 73°F. Norwesco says these tanks are for water storage only, not chemicals or fertilizer.
• Premium grade: rated for a specific gravity up to 1.5, or 12.5 pounds per gallon.

Norwesco adds that warmer liquid substantially lowers those ratings.

On color, Norwesco says most tank colors only identify the product type. The exception is its black and dark green water tanks, where the dark color limits light getting in and so reduces water-borne algae. Its standard above-ground water tanks are natural or white.

Is it safe for drinking water?

Norwesco says its above-ground water tanks are made from a linear high-density polyethylene whose resin meets FDA specifications for potable water storage. NSF 61 certification applies where listed and is granted plant by plant; Norwesco's FAQ names six plants, though its sentence says five, so confirm the certification for the exact tank and plant with the distributor if your use requires it.

CDC's emergency water guidance points the same way: use FDA-approved food-grade containers, and ask the manufacturer if you are not sure a container is food-grade. Never reuse a tank that held chemicals, fertilizer or fuel for drinking water.

Heat, cold, sun and weight

• Heat: Norwesco gives polyethylene tanks a 120°F maximum storage temperature; hotter contents can weaken and deform the tank.
• Cold: the tank has no minimum temperature, but if water may freeze, leave room for expansion. Norwesco says the bulkhead fitting is the most likely crack point and can be replaced.
• Sun: the resin is UV stabilized, but a shaded or indoor spot extends tank life. CDC also says to keep stored water out of direct sunlight, ideally at 50 to 70°F.
• No burying: above-ground tanks cannot go underground; the weight of soil collapses the walls.
• Weight: water-grade ratings imply water at about 8.4 pounds per gallon (9.2 / 1.1). A full 165 gallon tank holds about 1,380 lb of water and a 500 gallon tank about 4,180 lb, so set it on a level, solid base.

Sizing and keeping the water fresh

CDC says to store at least 1 gallon per person per day for 3 days, and a 2-week supply if possible, with more for pregnant women, people who are sick, pets and hot climates. Two weeks for a family of four is 56 gallons (4 x 14), about 468 lb of water, which a 120 or 165 gallon tank covers with room to spare.

CDC's storage rules for water you fill yourself:

• Label it "drinking water" with the date, and replace it every 6 months.
• Keep it away from toxic substances such as gasoline and pesticides.
• Use a clean scoop or tap each time you draw water.
• Keep unscented household bleach with 5 to 9% sodium hypochlorite on hand for disinfecting and sanitizing.

CDC's container-cleaning steps (wash, then sanitize with 1 teaspoon of that bleach per quart of water) are written for portable containers; for a large tank, ask the tank maker or distributor for a cleaning method. Norwesco sells through distributors and lists a 3-year warranty from the date of manufacture, which is embossed near the fill opening on tanks of 100 gallons or more.

What to look for when you buy

Questions people ask

Are poly water tanks safe for drinking water?

Food-grade ones are. Norwesco says its water tank resin meets FDA specifications for potable water, and CDC recommends FDA-approved food-grade containers for stored water.

Why are some water tanks black or green?

Norwesco says the dark color limits light penetration, which reduces the growth of water-borne algae.

Can a poly water tank freeze?

Norwesco gives the tank no minimum temperature but says to leave room for expansion; the bulkhead fitting is the most likely part to crack.

How often should I change stored water?

CDC says to replace water you store yourself every 6 months and to label it with the date.

Sources

• Above ground tanks frequently asked questions, Norwesco
• Black or dark green vertical water tanks, Norwesco
• Horizontal leg tanks, Norwesco
• Pickup truck tanks, Norwesco
• Specialty water hauling tanks, Norwesco
• How to create an emergency water supply, U.S. Centers for Disease Control and Prevention

Sources checked 2026-10-15.