While traditional Australian water tanks that collect rainwater are made of corrugated metal, there are other options that are much more visually appealing or even invisible.
The simplest rainwater tanks are rain barrels, which you can install yourself. For a hundred dollars, you can pick up these 80 gallon plastic barrels and hook them up to your gutter system. For larger systems or more elaborate installations, material is much more important.
A common tank material is polyethylene (poly), often food-grade plastic that’s stabilised to withstand UV exposure. All you need is a flat sandy base on which to place them. Poly water tanks come in a variety of colors to suit your aesthetic sense or house decor. Note that if you find a hot pink model, it may be wise to consult other residents of your dwelling prior to installation. Regardless of color, poly tanks generally last upwards of 15 years, and they can be recycled at the end of their lifespan. You should not count on them as a reliable source of firefighting water, since they’re made of plastic.
Galvanized steel tanks are the cheapest and oldest type of rainwater tanks. Galvanizing involves coating steel with zinc to slow corrosion, but a galvanized tank may still last less than five years… especially if the roof of your house or shed is made of zincalume, which creates an electrolytic reaction with the tank as the water drains from roof to tank. Zincalume and colorbond are improvements that add alloying metals and baked on primer layers to improve tank lifetime.