The maths is pretty simple to understand and so are the benefits. If you purchase a 110,000L Steel-Liner water tank, you will need to purchase at least 4 Poly tanks to come close to being able to harvest and store the same volume of water each year. With an approximate cost of $4,000 for an average 25,000l Poly tank, you would need to outlay $16,000 for 100,000l storage capacity, whereas a lined-Steel tank of 110,000l will set you back approximately just over half of this amount!
As you can tell from the table, the smaller tanks are more commonly manufactured with Polyethylene as it’s light and can be made relatively cheaply. For tanks between 1,000 Litres and up to 17,000 Litres, a poly tank is often your best choice and will set you back between $500 and $4,000. Things get a bit more complicated as tank sizes increase and this is where lined steel tanks become the more logical and common choice, particularly in high fire risk zones. Read more about Managing your water tank in a bushfire situation HERE.
The reason for this is is that for tanks up to around 17,000 litres, the price per litre of poly water tanks decreases as they get larger, as you might expect. At around this range, as tank sizes increase, the scales tip back the other way and the cost of poly tanks actually begins to rise again, making steel the better choice.
The main reason for this is the logistics and complications related to transporting tanks to site. Poly tanks in excess of 24,500 litres are considered oversize loads in many places in Australia and this places an increasing cost on delivery. Also, Poly tanks are made in moulds and it becomes impractical and expensive to manufacture moulds over a certain size.
Steel tanks, on the other hand are transported on a flat-pack pallet and are fully assembled on-site, which makes them easy to get to even the most remote and inaccessible sites.
No tanks are completely fire-proof, however, steel tanks offer better fire resistance than other products. Low heat bush-fire exposure can make steel tanks turn black on the outside, however, many steel-liner water tanks have remained intact when exposed to bushfire incidents throughout Australia.
Of course, prolonged exposure to high temperatures (such as experienced in an extreme fire-front) will eventually destroy most water tanks, depending on how much water is in the tank and the intensity of the fire.
Plastic tanks are known to catch on fire when there is a sustained ignition source, such as in a high intensity bush fire. Also, plastic-coated steel tanks, contrary to what some tank manufacturers state, are also sensitive to temperature. In an intense fire, the plastic coating inside the tank will separate and render the tank useless.
In research conducted by the CSIRO into Fire Impact, steel liner tanks performed better than Aquaplate®, with the steel-coating melting at about 200 degrees and fibreglass tanks also failed extensively.
Heritage Water Tanks are designed to resist damage to their structural integrity and retain water during and after exposure to a fire front. Examples of this were observed following catastrophic bush-fires in Victoria in 2009.
Lined steel water tanks are seen more and more widely in rural, domestic and commercial and industrial contexts and are available in all sizes, from smaller household tanks from 17,000l, through to tanks of up to several megalitres.
