Water Tanks Compared: Poly Tanks versus Galvanised Steel Tanks

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Poly Tanks vs Galvanised Steel TanksOne of the most popular choices today for storing rainwater is polyethylene (poly) water tanks. Another choice you might come across when selecting a rainwater tank are thick galvanized steel tanks.

Water tanks made today from galvanised steel are often thickly coated with a zinc alloy. This protects the inner steel from rust and corrosion.

In this article we compare key differences between poly water tanks and galvanised steel tanks, including how long it will last, strength, maintenance, installation and price.

Ease of installation

Poly tanks are easier to put in place and install. There are no incompatibility issues with dissimilar metals and materials that can cause corrosion (roof, gutters, treated timbers and fittings).

If you decide to re-locate a poly water tank, then you can easily do so provided you have help to lift the tank. Re-locating galvanised steel tanks are a much more difficult task and care needs to be taken not to tare or damage the inner poly lining.

Firm concrete foundations are ideal for all tanks, however bases can often consist of crusher dust for poly tanks. Galvanised steel tanks require more compact and solid foundations due to their construction.


Poly water tanks will often outlast a galvanised steel tank provided they are UV-stabilised to prevent the plastic becoming brittle in the Sun. The main maintenance issues with galvanised steel tanks are rust and corrosion, and they need an inner poly lining which helps to protect against inner corrosion.

The inner poly lining is not included in the steel tank warranty, and a one year warranty for the poly lining is common.


Poly tanks require much less ongoing expense to maintain, and can be setup with a tank self-cleaning system. With galvanised steel tanks, care needs to be taken not to rip the inner poly lining while cleaning, and welded joints and incompatible steel roofs, gutters and fittings can introduce weaknesses. Anodes (positively charged electrodes that carry electrons from a device) normally need to be replaced every 10 years.

Water quality

Corrugated steel tanks require an inner poly lining which helps to protect against inner corrosion and particles tainting the water. This also stops zinc leaching into the water which causes an unpleasant metallic taste. Poly water tanks manufactured from food-grade polyethylene provides the purest quality water and often at much cooler temperatures.


Galvanised steel tanks are very strong and will not bulge or warp since they are made from steel. Being metal however, they are less impact resistant than a poly tank which will easily withstand being struck with a hammer.

A weak point in the steel tank however, is with the thin inner poly lining which can be easily damaged when installing, tare and need repair or replacing.

Poly tanks can also be made very strong. It is a myth that all poly tanks bulge, warp and stretch. If properly designed and manufactured according to Australian standards for poly tanks then this should never happen. For example, strength is added through:

  • one piece construction (poly tank moulded at one piece without side seams)
  • if walls greater than 4.5mm and a strong base
  • tapered walls (thicker poly walls at the base)
  • ribs are added which help provide extra strength.

Requirements for building a strong poly tank are found in the Australian poly tank standard, AS/NZS 4766 Polyethylene storage tanks for water and chemicals. Note: Not all Australians poly water tanks comply with this standard. Always confirm your tank is certified by asking the manufacturer who certified them and for their certification number.


Steel tanks can be manufactured to higher capacities than poly tanks. Whereas poly tanks can be made to reliably store water up to around 50,000 litres, a steel tank can be constructed to store up to around 300,000 litres. That said, poly tanks can be coupled together to provide a combined capacity.


Poly tanks provide a greater variety of colours and styles to choose from than many galvanised steel tanks. To obtain a coloured galvanised steel tank is more expensive.


Poly tanks are cheaper to buy than a high-quality galvanised steel tank (with a zinc coating of 450 g/m2). Approximately 35% cheaper, but this depends upon size, type, colour and brand of tank purchased.

Team Poly Water Tanks

Team Poly are experts in manufacturing poly products. Our range includes rainwater tanks, industrial tanks and farming products. If you have found this article helpful, why not contact us today to discuss your needs.