One of the most popular tank choices today are polyethylene (poly) water tanks. Another choice you might come across when selecting a rainwater tank is BlueScope Steel’s AQUAPLATE® steel tanks.
Water tanks made from AQUAPLATE® steel sheets are made from ZINCALUME® steel (normally the older AZ150 rather than more durable newer generation AM125) that is thickly coated with a zinc alloy. Depending upon your AQUAPLATE® steel product, the ZINCALUME® steel sheet is then hot-dipped coated with either 450g/m2 zinc (unpainted sheets) or 275g/m2 zinc (COLORBOND® exterior colour or double-sided polymer laminate).
AQUAPLATE® steel was specifically created to be used in water tanks, and is the only product that BlueScope Steel recommends for water storage. Given this, AQUAPLATE® steel is recommend over a ZINCALUME® steel tank, and given AQUAPLATE®’s additional thick zinc coating, it offers greater protection than a traditional high-quality galvanised water tank.
In this article we compare key important differences between poly water tanks and AQUAPLATE® steel tanks, including how long it will last, strength, maintenance, installation and price.
Ease of Installation
Firm foundations are ideal for all tanks, however bases can often consist of crusher dust for poly tanks. Steel tanks require more compact and solid foundations due to their construction.
When it comes to installation, poly tanks are much easier to set in place than AQUAPLATE® steel tanks. If you also decide to re-locate your tank later on, then a poly water tank is much easier to move. Re-locating steel tanks is a much more difficult task and care needs to be taken not to damage the inner poly lining, base or walls.
Poly water tanks can last a long time, up to 20 years or more. The material can withstand the harsh effects of the Sun due to UV-stabalisers added to the moulding mix. These stabilisers inhibit or absorb the harmful UV light preventing the polymer from breaking down and becoming brittle.
With steel tanks, the number one issue is preventing rust and corrosion. AQUAPLATE® steel tanks have an inner polymer lining to protect them. If damaged, then water can easily cause rust and bubbling under the plastic coating. If caught however, then it can be cleaned and professionally recoated.
In addition, there are many chemicals, metals and other substances that AQUAPLATE® steel cannot come into contact with or corrosion will quickly occur. These include chemical agents, soil, ash, fertilizer, moisture, lead or copper and other dissimilar metals, water from copper flashings or copper pipes, and green or treated timber.
AQUAPLATE® steel tanks normally come with a comparable warranty to poly water tanks, however it is important to be aware of the conditions as AQUAPLATE® steel can be quite sensitive to external factors.
For example, sample warranty conditions (PDF) by BlueScope for AQUAPLATE® steel tanks state warranty will be voided for each of the following:
- tanks placed within 500m of sale marine, heavy industrial of other unusually corrosive influences
- damage is caused by water from the overflow outlet falling onto the tank (the overflow is often a weak point especially if the hole has been cut out incorrectly)
- failure to remove debris and/or allow free drainage of water and removal of condensation
- corrosion caused due to not washing down the tank
- accidental damage caused by a person or animal
- contact with soil, ash, fertilizer, moisture, lead, copper and other dissimilar metals, chemical agents, runoff from copper flashing or copper pipes, treated timber (for more information, refer to Corrosion Technical Bulletin CTB-12 “Dissimilar Metals” and CTB-13 “Contact with Timber”).
Polymer water tanks are more resilient and not as sensitive to external factors.
Poly tanks require much less ongoing expense to maintain, and can be setup with a tank self-cleaning system. With AQUAPLATE® steel tanks, care needs to be taken not to damage the inner poly lining while cleaning, and welded joints and incompatible steel roofs, gutters and fittings can introduce weaknesses.
AQUAPLATE® steel tanks are fabricated with 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 provide the purest quality water and often at much cooler temperatures.
AQUAPLATE® steel tanks are very strong and will not bulge or warp since they are made from steel. While steel is a strong material, it is also less impact resistant than a polymer tank which will easily withstand being struck with a hammer.
With AQUAPLATE® steel tanks you also need to ensure its poly lining (about 0.2mm in thickness) does not become scratched or damaged. Care must be taken in installation, and many sellers state your warranty will be voided unless you use an authorised installer.
Poly tanks are also very strong. If properly designed and manufactured according to Australian standards for poly tanks then bulging and warping should never happen. Some features of a strong and quality poly tank include:
- It being moulded as one seamless piece (that is, without side seams)
- Wall thickness being of 4.5mm or greater
- Strong base corners with a radius of 25mm for a tank up to 1.8m in diameter, or a radius of 38mm for tanks over 1.8m in diameter.
- Tapered tank walls (thicker poly walls at the base of your tank where the most pressure will be)
- Ribs which provide greater strength.
Additional 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.
AQUAPLATE® 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.
AQUAPLATE® steel tanks, like many poly water tanks, offer a range of COLORBOND® colours to choose from. Steel tanks can often be specially constructed if need be, as can poly water tanks. Each have comparable shapes, your traditional round and slimline.
Poly tanks offer greater versatility with tank options that can be placed in moisture prone areas such as under a deck and or underground. Given the weaknesses to moisture, these options are simply not possible with AQUAPLATE® steel.
Poly tanks are cheaper to buy than an AQUAPLATE® steel tank. Approximately 25% cheaper, but this is dependent 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.