Steel is an excellent material for rainwater tank construction, providing strength, longevity and security against algae, mosquito larvae and other outside contaminants. However, if you are having a steel rainwater tank fabricated to order, you may be overwhelmed by the dizzying array of choices and configurations available to you. As such, you should keep the following things in mind while specifying your new tank to make sure it fits your needs as closely as possible.
How large should my tank be?
For steel rainwater tanks, bigger is not always better, and the cost of fabricating a steel tank tends to rise exponentially as you go larger. Aside from the added steel required to make a taller or wider tank, the increased weight of the added water capacity requires thicker steel that is more expensive and difficult to weld.
As such, you should try to calculate the maximum amount of water your tank is likely to collect before you need to use it. On farms and other commercial operations requiring extensive irrigation this can be quite large, but a tank made to collect water for smaller flowerbeds and vegetable gardens will obviously require much less capacity. However, you should also consider whether to add extra capacity to serve as an emergency water reserve, particularly in parts of Australia vulnerable to droughts.
Should I choose corrugated steel?
While many steel rainwater tanks are made from conventional flat sheet metal, more heavy duty tanks tend to be made from corrugated steel. This is for a couple of reasons; corrugated steel has considerably more strength against both internal water pressure and external impact damage, and is also highly resistant to buckling and distortion caused by earthquakes, land slippage and other natural hazards.
However, corrugated steel costs considerably more to use than flat sheet metal because of the added costs and materials used in creating it, so it may only be worth going corrugated if your tank will be used in a busy, heavy-duty environment such as intensive farming.
Should I have my tank coated?
Steel naturally rusts and corrodes when exposed to moisture, and any steel rainwater tank should be fitted with an internal liner made of PVC or other inert materials at the very least. However, you may also want to consider having the steel itself covered with a protective coating, which increases its resistance to rust caused by both internal and external moisture, increasing the longevity of your tank. You have a number of coatings to choose from here:
Powder coatings are made from tough, rustproof epoxy resins that are baked onto the surface of the tank in powder form. Many steel fabricators offer this highly effective protective coating, but it can be expensive.
Galvanised coatings are cheaper, and leave a thin coating of zinc on the surface of the tank, which acts as an effective rust barrier. However, galvanised coatings have a limited shelf life and must be renewed periodically, which is a difficult proposition when dealing with a large and unwieldy rainwater tank.
Bitumen coatings can be added to galvanised steel to provide an added layer of protection and is also available in non-toxic varieties suitable for storing potable water. However, this double coating can be expensive, and not all fabricators offer this service.