First published December 2007, updated April 2011
Drought is a part of normal life in many parts of the world and given the
threats posed by climate change, place with traditionally low rainfall may
become even dryer and long established rain patterns give way to major rain
events - a feast or famine scenario. A way to better utilize the feast to help
through the lean times, or in other disasters where mains supply may be cut or
contaminated is to install a rainwater tank
Here in Australia, the corrugated metal 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 regard to larger tanks where construction is a more important aspect, 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 and you only need a sand base to place them on. They come in
a wide variety of colors, usually molded into the plastic, and have a long serviceable life. Many poly tanks
carrying a 25 year warranty, although many claim 15 years is a more 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 will
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 to a
recycler.
Some poly tanks are made with a vertical seam - this is a weak point that
may cause splitting and subsequent water loss - so a seamless tank is probably
a better choice. Polyethylene water tanks and
fire don't really mix either as they'll just melt should the flames get too
close. 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 performed in relation to these
issues as far as I know.
I had a polyethylene rainwater tank at my original place in the outback where
temperatures would get up to around 46C (115F) degrees Celsius 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). A subsequent poly
tank I acquired for my current property has also stood up well to similar
extremes - and without the odd taste being added to the water.
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 slow
down
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 - but the same goes for any material.
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
or gel coat applied.
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 regard 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.
A brief note on rainwater tank regulations
Regardless of the material you settle on, before buying and installing a
tank you should check with your local authorities as in some places you will
need a special permit and in others they may be totally banned - which is
absolutely ridiculous in my opinion. Even in Australia, the driest inhabited
continent on Earth, some local governments had bans in place until relatively
recently - but the Millennium Drought thankfully sorted out most of those
short-sighted councils.
Australia wasn't the only country with crazy laws regarding rainwater
harvesting. Up until 2009, in Colorado in the USA, it was illegal
for households to capture rainwater as rights to water were allocated in the
state; i.e, that water that fell from the sky was owned/leased by other parties.
I'm pleased that sanity prevailed in that case also; but no doubt there are
still some regions where similar silly legislation is still in place. If you're
unfortunate enough to live in such an area, consider organising protest action
rather than letting the status quo remain.
