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Water Tanks Compared: Poly Tanks versus ZINCALUME® Steel Tanks

Water Tanks Compared: Poly Tanks versus ZINCALUME® Steel TanksOne of the most popular choices today for storing rainwater are polyethylene (poly) water tanks. Another choice you might come across when deciding on a rainwater tank is ZINCALUME® steel (a mixture of zinc and aluminium).

Tanks made from ZINCALUME® steel, are made from a steel that has been dipped in aluminium (55%), zinc (43.5%) and a bit of silicon (1.5%). This protects the steel from rust and corrosion in two ways:

  1. It provides a tough physical barrier to protect the inner core steel against the weather, and
  2. It protects the steel if cut at its edges and/or scratched.

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

Ease of Installation

Poly tanks are easier to install than ZINCALUME® steel tanks. Poly tanks have no incompatibility issues with dissimilar metals and materials that can cause corrosion. ZINCALUME® steel tanks require more complication installation and you need to ensure compatible roofing, gutters, pipes 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 ZINCALUME® steel tanks normally needs to be done by your supplier or an authorised representative or your warranty will be void.

Firm concrete foundations are ideal for all tanks, however bases can often consist of crusher dust for poly tanks. ZINCALUME® steel tanks require more compact and solid foundations.


Poly water tanks will often outlast a ZINCALUME® steel tank provided they are UV-stabilised to prevent the plastic becoming brittle in the Sun. The main issues for ZINCALUME® steel tanks are that great care needs to be taken to prevent corrosion and the inner poly lining.

Moisture needs to be kept at a minimum which is hard to do when on the ground. It needs to be kept free from treated timber, leaves and plants, and it reacts to copper and lead.

The inner poly lining is not included in the steel tank warranty, and a one year warranty for the poly lining is common. Furthermore, this poly lining can also cause water to condense between it and the inner steel wall which creates unhealthy moisture for the ZINCALUME® steel.


Poly tanks require much less ongoing expense to maintain, and can be setup with a tank self-cleaning system. With ZINCALUME® 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

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


ZINCALUME® 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, tear 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 chemicalsNote: 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.


ZINCALUME® 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 hundreds of thousands of litres. That said, poly tanks can be coupled together to provide a combined capacity.


ZINCALUME® steel tanks can be easily painted, but an approved paint must be used. Poly tanks come in a variety of colours and styles to choose from.


Poly tanks are cheaper to buy than ZINCALUME® steel tanks, approximately 20% cheaper depending upon the size and brand being 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.