Poly Water Tanks or Steel Water Tanks

Poly vs Steel Water Tanks

For many people who are either investing in, or upgrading their water tank or water storage capacity, the choice is between Poly or Steel Water tanks. To help aid you with this decision, we’ve compiled a few of these differences below.

Steel Water Tanks

Typically Steel Water Tanks are made from Galvanised Steel, Colorbond® Steel or Zincalume® Steel, and are the more traditional style tanks people would be used to seeing in rural environments around Australia.

Steel Water Tanks are typically pre-fabricated and constructed on site, and transported in flat packs to the location. Steel tanks need to be built on a prepared sand pad with aggregate surrounding it to ensure that there is no shifting or falling that occurs, as this would destabilise the tank.

Thanks to the bolt together modular design of steel water tanks, they can be constructed up to much larger capacities than poly water tanks can. Typically the larger volume of water storage is required, the more economically feasible it becomes to invest in a steel water tank.

If the tank is to be used for potable water, a steel tank would require a liner, which keeps the water fresh, and prevents corrosion of the zinc alloys in the metal of the tank. All liners are designed to food grade standards for products that come in contact with drinking water.

Poly Water Tanks

Poly Water Tanks or Plastic Tanks are typically constructed from polyethylene plastic, which is a food grade material, and means the tanks to not require a liner. The Polyethylene is typically UV stabilised to ensure that the plastic does not break down in the sun.

Poly tanks are transported to the location fully built, and are usually constructed in one piece, or two pieces with a welded seam down the middle. the most typical poly water tank purchases are between 20,000L and 25,000L, but they can be manufactured up to 50,000L in some circumstances.

Poly tanks are typically easily repairable by a trained plastic fabricator, a service which most suppliers also offer throughout the service life of your tank.

Lifespan and Longevity

Thanks to the UV Stabilisation techniques used, poly water tanks last much longer than typical plastics would when exposed to the elements, however because the plastic is used to hold water, there are limits to how many of these chemicals that can be added. This means that the tanks will still slowly deteriorate over time.

Steel water tanks have a longer life span typically than poly water tanks, as the steel does not get degraded by sunlight. However, steel tanks without a liner that interact with water with high salt or chemical contet may corrode faster than those with a liner if not treated or galvanised correctly. All Southern Cross Water Tanks come with a 10 year warranty.

Fire Protection and Fire Resistance

While both steel water tanks and poly water tanks can be used as fire tanks and for fire protection, only one is truly fire resistant. When exposed to a fire font, poly water tanks will melt and buckle under the force of the heat, as the plastic deteriorates, which will make the tanks unusable after that point.

Steel water tanks resist fire, and often continue to hold water after a fire front has passed, which can be crucial to fire fighting efforts. If a steel water storage tank is equipped with a liner, the liner may not be able to hold up under the intense heat, and it is important that a tank installer or expert inspect the water tank before it continues to be used for potable water.

Environmental Impact

At the end of their service life, there is considerable differences with how steel water tanks and plastic water tanks can be repurposed or disposed of.

As steel water tanks are made from steel alloys, once they have outlived their usefulness, the steel can be melted down and recycled to create a variety of other products.

Poly water tanks however, pose a much more difficult issue at the end of their functional life. As the main reason for poly tanks needing to be disposed of is the degradation of the plastic, this means it is difficult to recycle and can only be repurposed into a very limited number of products. Poly water tanks typically end up in landfill.

Colours and Design

Due to the moulding process of poly water tanks, they are able to be made in a variety of shapes and sizes, allowing some access to rainwater even for people with limited space, thanks to slimline and other varieties of water tank.

Steel water tanks however typically are only available in the larger round tanks, but are typically available in all standard Colorbond® colours either bonded to the sheets, or factory powder coated to the tank sheets before construction.

The Verdict

Poly water tanks are more suitable for people looking for a cheaper option, who are either challenged for space, or looking for a smaller amount of water storage. As the need for larger volumes of water increases, or if the tank is for fire protection or a long term investment, steel water tanks become the more viable option.

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