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500 gallon water tank: plan the complete water reserve

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

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Quick answer

Choose a 500 gallon water tank around its installed footprint, filled load and drinking-water plan. Norwesco lists its black 43101 at 48 in diameter and 73 in height, with a 16 in lid and 1.5 in outlet. Using the USGS approximate water weight of 8.33 lb per gallon, 500 gallons adds about 4,165 lb before the tank and fittings. Its potable-water resin specification does not establish that any water placed inside is safe. Verify the exact tank, site support, fittings and cleaning process before filling.

Decide what the reserve is meant to cover

A 500 gallon water storage tank is a large container, not a complete drinking-water system. Decide whether it will hold a known safe supply for household use, non-potable water for another purpose or incoming water that needs an assessed treatment process. Keep those uses clear when selecting the tank and marking the stored water.

Ready.gov advises at least one gallon per person per day for several days, for drinking and sanitation. It also says needs vary with health, activity and climate. Use that baseline for an initial reserve calculation, then account for your household rather than assuming the tank replaces normal household water use.

For a hypothetical four-person household at one gallon each per day, 500 divided by four is 125 days of baseline volume. This assumes every nominal gallon is usable and no losses or additional needs. It is arithmetic, not a promise of safe storage life or a guarantee that the tank meets all daily water demand.

Access matters as much as volume. Include a way to withdraw water into clean containers and a practical refill and rotation plan. A reserve that cannot be reached or safely maintained is incomplete, even if the capacity looks sufficient.

Read the current tank specifications and their limits

Norwesco current water-tank listing	500 gallon example	What to verify
Black part number	43101	Exact model and delivered configuration
Dark green part number	43105	Color and model identity
Diameter / height	48 / 73 in	Route, installed space and lid access
Lid	16 in	Matching closure and maintenance access
Listed outlet	1.5 in	Actual fitting, threads and supported accessories
Listed bulkhead fitting	2 in	Do not confuse it with the outlet label

The maker says these black or dark green tanks use resin meeting FDA specifications for potable-water storage. Dark color limits light penetration and reduces algae growth. Neither statement is a treatment claim or a guarantee that algae can never develop.

Norwesco describes this range as water-storage-only equipment. Its 9.2 lb per gallon rating is a liquid-density design limit, not the weight of drinking water or permission to use chemicals or fertilizer in the tank.

The current page links a general 500 gallon vertical drawing with a July 2013 revision. That drawing shows a 70.5 in overall axial dimension, while the current water-tank table lists 73 in height. The drawing does not identify 43101 in its title block. Do not silently choose the smaller dimension; obtain current, model-specific confirmation for a tight installation.

Plan for water weight, access and the correct installation

USGS lists approximately 8.33 lb per gallon for water. Multiplying 500 by 8.33 gives 4,165 lb of water alone. Add the actual tank, fittings and any supported equipment when checking the site. This approximate calculation is not a structural design load or permission to put a full tank on a deck, shelf or elevated stand.

Before delivery, ask the tank maker for the exact installation requirements and have the proposed support assessed for the complete load. Do not invent a pad thickness from the gallon capacity. Check the delivery route and working room around the tank, including access to the lid and outlet for maintenance.

Norwesco explicitly prohibits burying an above-ground tank. It says surrounding earth can collapse the walls. If the site requires an underground cistern, choose equipment expressly designed and approved for that installation rather than using this above-ground example.

The maker also warns that freezing contents need room to expand and that the bulkhead fitting can crack. No universal headspace percentage is given in the opened FAQ. Obtain the appropriate local freeze-protection and fill guidance; a tank surviving outside does not establish an accessible, unfrozen water supply.

The water-storage designation does not establish approval to use the tank as a pressure vessel. Have any pump, plumbing or connection to building water systems assessed as a complete arrangement. Do not infer safe pressure or transport use from the storage capacity.

Keep the drinking-water chain intact

CDC recommends food-grade water storage containers and warns against using containers that previously held toxic chemicals. Confirm the tank and every water-contact component for the intended potable use. An unknown used chemical vessel is not an equivalent substitute for a documented water tank.

Norwesco says NSF61 certification applies where applicable and depends on the manufacturing plant. Its FAQ is inconsistent about the count of certified facilities. That does not establish certification for every individual tank. Ask for the exact tank and plant documentation if a certification is required for your installation.

Confirm a suitable cleaning and sanitizing procedure with the tank maker before the first fill. CDC's small-container instructions include shaking solution over the interior. Do not improvise a way to shake a large tank or assume a bottle procedure validates a bulk installation. Get a practical method that reaches the required water-contact surfaces.

CDC advises labeling stored drinking water with the date, replacing self-filled water every six months and avoiding sunlight and toxic substances. Keep withdrawal containers clean and avoid touching the stored water with hands.

Storage color is not a water-treatment system

Begin with a known safe supply and maintain its handling chain. If the incoming water is not established as potable, have its quality and treatment requirements assessed. A dark tank, an attractive appearance or a sediment screen does not establish that the water is suitable for drinking.

CDC says portable filters do not remove every type of germ and directs people to follow health-department recommendations for unsafe water. More importantly, water containing fuel, toxic chemicals or radioactive materials cannot be made safe by boiling or disinfecting. Use another safe source and seek public-health advice if that contamination is known or suspected.

A treatment product must be matched to the actual water condition and its labeled process. Do not put an arbitrary amount of bleach into a nominally full tank or assume an aquarium or irrigation accessory provides drinking-water treatment. This page does not supply a bulk dosing recipe.

Keep a separate accessible supply while the large reserve is being cleaned, checked or refilled. CDC identifies unopened commercially bottled water as a reliable emergency option. The large tank and smaller ready-to-use water can serve different parts of the same preparation plan.

Inspect the Amazon offer as a complete storage purchase

Check the actual model, water-use documentation, dimensions, lid and included fittings. The Norwesco current table distinguishes the outlet from the bulkhead fitting; a listing that mentions only a connection diameter leaves important details unanswered.

Ask whether the offer includes the intended valve and other accessories, and confirm the delivery and placement arrangements before purchase. These Amazon searches identify documented equipment or component criteria. They do not establish current tank availability or include a promise that a generic valve will fit.

• Match the tank to the intended potable or non-potable use.
• Resolve the model-specific dimensional discrepancy.
• Verify complete filled load and installation requirements.
• Confirm supported water-contact fittings and withdrawal method.
• Arrange cleaning, refill, freeze protection and dated rotation.

The general water-storage guide covers reserve planning across container sizes. For this capacity, use the specific footprint and load checks above before turning a gallon target into an installation.

What to look for when you buy

Questions people ask

How much does a full 500 gallon water tank weigh?

Using the USGS approximate water weight of 8.33 lb per gallon, the water alone is about 4,165 lb. Add the actual tank and fittings. Have the full installation assessed; this calculation does not certify a support structure.

How long does 500 gallons of water last?

At Ready.gov's initial one-gallon-per-person daily baseline, a hypothetical four-person household divides 500 by four to get 125 days. That assumes fully usable volume and no additional demand or losses. It does not establish safe storage life.

Can I bury the Norwesco above-ground tank?

No. Norwesco says above-ground tanks cannot be installed underground because earth pressure can collapse them. Use an expressly designed underground cistern if that is the intended installation.

Does a black potable-water tank make rainwater safe to drink?

The tank material and dark color do not validate the incoming water. Have the source and any treatment system assessed. CDC warns that boiling or disinfecting cannot make fuel- or toxic-chemical-contaminated water safe.

Sources

• Black or Dark Green Water Tanks, current table, Norwesco
• Above Ground Tanks Frequently Asked Questions, Norwesco
• 500 Gallon Vertical Tank drawing, revision July 2013, Norwesco
• Water: needs and storage, Ready.gov
• Facts About Water, U.S. Geological Survey
• How to Create an Emergency Water Supply, CDC
• How to Make Water Safe in an Emergency, CDC

Sources checked 2026-10-14.