When it does rain here, which isn't all that often these days, it's a happy experience mixed with guilt. Unlike previous houses I've lived in, we have no rainwater tank at present. Watching those gallons of precious clean water pouring away makes me feel very un-green.

Here in Australia, the corrugated rainwater tank is somewhat of a national icon. In South Australia, around 30% of homes have rainwater catchment systems. Water tanks haven't been an overly attractive home addition until recently; although seeing the old style tank does make me feel very nostalgic! These days, tanks come in all sorts of shapes, colors, materials and sizes to suit any home and space.

Even if having a full size water tank isn't an option for you, rain barrels are a very cheap and easy to install option. These look like a pickle barrel, are mostly made of plastic and hold up to 80 gallons - you can pick them up for around a hundred dollars. Ever gallon of water saved counts!

In regards to larger tanks, in this article, we'll take a brief look at the various materials commonly used, their advantages and disadvantages.

Poly (plastic) rainwater tanks

Poly tanks are made from polyethylene; a UV stabilized, food grade plastic. The tanks are light, you only need a sand base to place them on, they come in a wide variety of colors and have a long serviceable life. Many poly tanks carrying a 25 year warranty, although many claim 15 years is a very realistic lifespan. They are also usually the second cheapest of the options covered in this article.

One of the major disadvantages of polyethylene is the material is made from petrochemicals. Even after their serviceable life has ended, there's still a great big hunk of plastic that will take generations to break down and wiil release toxins as it does so.

However, polyethylene tanks can still be easily recycled after 15 years, so it's just a matter of breaking the tank up and then carting it away rather than trying to squeeze a few more years out of one.

Some poly tanks are made with a vertical seam - this is a weak point that may cause splitting and subsequent water loss. Polyethylene water tanks and fire don't really mix either - they'll just melt. This can be a real problem if you're in a rural area and you need that water to fight a fire.

The other issue is the long term effects of drinking water stored for such a long time in this material. Polyethylene tanks are relatively new on the market, so there's no serviceable life studies been done in relation to these issues as far as I know.

I had a polyethylene rainwater tank at my place in the outback where temperatures would get up to around 46C (115F) degrees celcius in the shade and below freezing during winter. The tank performed well over the couple of years I had it before selling the property, but there was a bit of an odd taste to the water on hot days (it was placed in full sun).

Just on that point - before purchasing a poly tank, check the warranty for temperature stipulations as some manufacturers will void the warranty if conditions where the tank is installed can get extremely hot.

Steel tanks

Three materials are most popular - Galvanized steel, Zincalume®  and Colorbond®  (the latter two may be called by other names in different countries).

Galvanized tanks have been around for over 150 years and are usually the cheapest type of tank. Hot-dip galvanizing is a process used to coat steel or iron with zinc. The Zinc helps slow down corrosion, but depending on environmental factors, a galvanized tank may last well under 5 years, particularly if the roof of the structure capturing the rainwater is made from Zincalume. This is due to electrolysis.

Zincalume®  has been around for about 30 years and was originally used for roofing. It's a a mix of 55% aluminium, 43.5% zinc and 1.5% silicon bonded to steel. There's a lot of conflicting information around about lifespan, but the general consensus seems to be about 10-15 years.

Colorbond is Zincalume with a conversion layer applied to the surface of the steel to improve adhesion; then a polyester primer baked on, followed by a top coat of paint that is also baked on. It's not unusual to find a 20 year warranty on these tanks, but a deep scratch to the paint can be enough to accelerate the corrosion process.

Some metal tanks now also have polyethylene linings to further help retard corrosion - escaping plastic altogether can be a difficult thing to do these days.

If you do buy a steel based tank, look into installing extra sacrificial anodes to further delay corrosion.

Concrete water tanks

Concrete rainwater tanks can be installed either above or under ground. The latter is a good option if you're short on space as they can be constructed in such a way to allow for load bearing, for example under a driveway.

Given the material, they are very heavy and often poured on-site or delivered in sections that are then basically cemented together. Again, a polyethylene liner may be used. Without a liner, the tank will leach lime and over time you'll have a slightly alkaline water. With concrete being porous, without a liner water will penetrate into the concrete over time which may cause corrosion problems in relation to steel framework.

Concrete is also an energy intensive product that requires a great deal of heat and water in its production. Additionally, the components need to be mined.

Fiberglass

This is another long-lasting option that can be installed above or below ground. Fiberglass tanks resist corrosion and are not generally affected by chemicals.

As fiberglass tanks tend to allow more light in than other types of tank materials, this can encourage the growth of algae, so they should be painted. Fiberglass can also tend to be brittle, leaving it prone to cracks - something you don't want, particularly in an in-ground situation.

Choosing a tank material

Choice is wonderful, but as you can see, there's advantages and disadvantages with each type of tank, particularly when it comes to environmental impact - so it's really a matter of gauging your needs and budget and then choosing the lesser of the evils. In regards to the financial side of things, bear in mind not just the initial cost, but how many times the tank will need replacing over X years. This also plays a role in the amount of resources used. Something worth checking into are rebates on rainwater tanks and/or associated plumbing - many governments now offer cash-back schemes.

Even with the various disadvantages of each material, given the length of serviceable life of most tank options and the tens of thousands of gallons of water you can collect over that time; installing a rainwater tank is still a very green move.