Underground Concrete Water Tanks – Your Definitive Guide

**Please note Versatile Tanks DO NOT repair water tanks**

Our climate in Australia means that the country can be extremely prone to water shortages and droughts, so being prepared should be considered a main priority for every home. Those living in more isolated and rural areas are most at risk but if you live in a city, you’re not out of danger either. Water shortages can affect everyone, even if you are hooked up to a municipal city supply.

Concrete water tanks can be buried deep underground, providing an instant solution to the age-old problem of water collection. Environmentally-friendly and simple to look after, they offer the easiest way of insuring against future water shortages.

If you’ve never considered having an underground concrete water tank before, here’s some more information about how they work and just why they’re so popular with homeowners.

About underground concrete water tanks

11700 litre medium tanks for JCUUnderground concrete water tanks aren’t a temporary structure; the job of installing them isn’t insignificant and should only be undertaken by properly qualified individuals who have carried out a thorough assessment.

Opting for an underground tank made from concrete isn’t the cheapest option in the short term but in the longer term is an extremely prudent investment. It could add value to the property and won’t need replacing as quickly as the cheaper plastic models. Investment costs can also be offset by potential available rebates.

Concrete is such a strong material that a vast number of options open up, allowing even small plots of land to benefit from having large underground reserves.

Rural households and agricultural operations have relied upon underground concrete tanks for some time but their many benefits are now being utilised by more urban districts too.

Why buy an underground concrete water tank

Water is such a precious commodity that it’s important to make provisions to ensure your household has a back-up supply, in the event of a shortage.

If you live in the country or in a remote location, the chances are that you won’t have access to a mainline supply, and will instead have to find your own water for all of your needs. Water tanks are the simplest and easiest way of storing water for when you need it, and underground is a much better option than above ground (but more about that below).

An underground concrete water tank provides you with the option of either transporting water in from elsewhere and storing it, or collecting rain water for use, or a combination of the two. Concrete tanks can be built much larger and there’s no risk of splits or leaks so you can store much greater volumes of water for when you need it, offering real peace of mind.

But the issue of water storage isn’t unique to rural locations, although it may be more frequently needed. Even if you have access to a municipal water supply, there’s no guarantee that there won’t be a shortage, or an interruption to your supply. Droughts and long periods of hot weather in Australia mean that hosepipe bans and water consumption limitations aren’t unusual, leaving you with no way to service a wilting garden or run the washing machine as often as you’d like.

Underground Concrete Water Tanks AustraliaA water tank is a means of supplementing the water supply that’s available on tap; an environmentally friendly way of ensuring that you can use what you want, when you need it, without restriction.

In addition, by using your own supply of water, you won’t just be helping to protect the environment, you’ll be saving your bank balance too. Reducing the amount of water you consume from your regular source could lower your bill, and by using your own reserves instead, you won’t even have to make any sacrifices.

An underground concrete water tank offers a year round supply of water that’s ready and waiting for when you need it.

In addition to all of the other benefits, having an underground concrete water tank helps to improve safety too. With its scorching temperatures and wooded areas, Australia is unfortunately prone to suffering from fires. Houses equipped with water tanks have a reserve that can be utilised to help get fires under control more quickly if and when the need arises.

Main differences between above ground and underground tanks

If you want the convenience of having your own water supply but with the minimum of hassle, you might think that an above ground tank is the obvious option. However, with underground water tanks offering a lot of different advantages, it’s a decision that’s worth considering in more detail.

The first, and most glaring, difference between above ground and underground tanks is the physical presence. Every 1000 litres of water takes up a cubic metre so a large tank could present quite a blot on the horizon and not everyone has the space for this. By moving the tank underground, it remains out of sight regardless of how large it is.

The other benefit is that installing an underground tank means that the water is kept much cooler, and this combined with the lack of light, means that algae growth is eliminated. This elongates the lifespan of equipment such as pumps and valves and ensures that the water quality remains high and suitable for use indoors, and not just in the garden.

Although Australia enjoys a warm climate, there are areas, particularly southern Victoria and Tasmania where cold periods are likely to occur, with temperatures plunging. If you have an above ground tank there’s the danger that the water will freeze unless you have an insulation system in place to prevent this. This can add considerably to the cost.

Underground tanks will take longer to install and will also be more expensive compared to above ground water tanks. However, this is just a short term cost as in the longer term, an underground tank could save more money. The life span of an above ground tank is limited while an underground tank, particularly in a durable material such as concrete is almost indefinite. Add to this the advantages such as temperature control and biological growth, and the economic advantages are significant.

Advantages of underground concrete tanks vs other materials

Once you’ve decided to invest in an underground water tank, you’ll decide to make a further choice about the type of material you want to use.

Plastic is one of the most common materials for water tanks, most typically polyethylene, and represents a cheap and easy option. It comes in a wide variety of shapes and sizes and because it doesn’t corrode, is great for locations that are close to the ocean and could be exposed to saline water.

When used underground, a bladder system is often used to provide a degree of strength. This involves a metal frame supporting a PVC, rubber or plastic bag. There’s a separate manufacturing standard for water tanks using a bladder system, AS/NZ4766:2006. Additional care needs to be taken to check that the material that’s used to manufacture the bladder is compatible with housing drinking water.

Despite this extra strength provided to poly plastic water tanks, they still are limited to relatively small dimensions. For any tank that’s intended to hold more than 10,000 litres, a stronger material is usually recommended.

The other downside to poly is that when it needs to be replaced – and it will because it has a limited lifespan – its recycling capability is seriously restricted. Very few products can be made from recycled poly, and most of it is destined to end up in landfill.

Steel tanks have become the modern replacement for the galvanised iron tanks that were offered in the past, and incorporate an inner lining made from a food-grade polymer. This is often known as Aquaplate.

Aquaplate tanks have a good durability and are often guaranteed for around twenty years, and may even last beyond this. They’re lightweight, that makes them easy to transport and to get into place. The membrane on the inside of the tank is resistant to corrosion so providing this isn’t damaged in any way, there’s no risk of rust.

Underground Water Tank - Versatile TanksCleaning and maintenance can damage the inner lining if proper care isn’t taken and this can cut short the lifespan of the water storage tanks. Careless installation or transport can also damage the interior so it should be carefully inspected.

If you want an underground tank, Aquaplate probably isn’t your best option because of its light weight. Ground water and flooding can cause tanks to rise up and float, especially when they’re empty unless they are solid enough to remain in place.

In contrast to both Aquaplate and plastic tanks, concrete is an incredible durable material. Most manufacturers will guarantee their tank for at least 30 years but you can expect it to last way beyond this.

Used in rural locations for many years, the advantages of using concrete have meant that it has rapidly become the material of choice in urban households too. Its strength and suitability for use underground has provided new options for water storage, enabling homeowners to install tanks under driveways or back yards.

Concrete tanks can be installed in very large sizes, providing a whole of house water solution that’s invisible and out of sight.

The water quality from concrete tanks is excellent and can be used for drinking. In addition, concrete keeps water much cooler than any other material so there’s far less likelihood of algae or other growth.

Because they’re designed to be load-bearing, concrete tanks are extremely sturdy and there’s no risk that they will rise up and out of position. They are also rust-proof, melt-proof and burn-proof so are the ideal material for areas that could be susceptible to fires.

There’s less choice over the shape of concrete tanks but this is gradually improving. Typically you can either buy a pre-cast size and shape, or opt for the casting to be completed on site.

Recycling is less of an issue because of the extreme durability of a concrete water tank, but if the need arises, concrete is an environmentally friendly material.

Manufacturing methods

The manufacture of underground concrete water tanks is more time consuming that other types of materials that can simply be dropped unto place. But once a concrete tank has been created, the extra work will be worth it because it’s extremely durable and will outlast more or less every other type of material.

This kind of investment can even add value to a property because it’s such a useful asset.

Underground Water Tank AustraliaConcrete water tanks can be formed onsite but we manufacture ours in a closed factory environment. The reason we choose to do this is that the natural environment can be so variable, it is impossible to be certain that the concrete will be exposed to exactly the right kind of conditions to ensure optimal formation. Manufacturing concrete water tanks onsite can result in micro cracks forming so it’s a less than ideal method to employ.

Manufacturing the material in our factory means that we can adapt the dimensions to what’s required, such as reducing the overall height or making the lid thicker.

Because underground water tanks may be required to weight bear, it’s important that they’re made from materials that are able to withstand a load. All our tanks are manufactured using high strength concrete created to a very exacting standard; this ensures that it cures quickly to the high strength required of 72MPa.

MPa (megapascals) is the way in that the strength of concrete is measured and replaces psi (pounds per square inch) as the assessment used in many countries in the world, including Australia.

As a general rule, anything with an MPa of more than 41 is considered as a high strength combination; 17 is the usual degree of MPa seen in most residential preparations. An MPa of more than 41 is deemed to be suitable for large constructions such as bridges and buildings. Around 40 years ago, 76 was thought to be the maximum MPa achievable, but that’s now known not to be the case and by 2010, buildings in the US had been created with an MPa of 131.

Our manufacturing process pours the concrete at strength of 50 and after being left to cure for 28 days achieves a full MPa strength of 72.

This figure demonstrates just how strong our concrete water tanks really are.

Popular sizes

Underground concrete water tanks come in a range of sizes and are available in large dimensions, suitable for providing whole house solutions.

We offer three main sizes for our underground concrete water tanks: 6700 litres, 11700 litres and 22500 litres.

– The 6700 water tank measures 2100mm in height by 2100mm in width and 1800mm in length and weighs in at 4.1 tonnes.
– The 11700 water tank measures 2400mm in height by 2400mm in width and 2400mm in length, a cube design, and weighs in at 7.1 tonnes.
– The 22500 water tank measures 2600mm in height by 2400mm in width and 4400mm in length and weighs in at 11.7 tonnes.

Benefits of underground concrete tanks

The advantages of having a water tank are undeniable but once you’ve made the decision to have one installed, there’s a choice to make about whether to place it and what materials to choose.

An underground concrete tank has a huge number of advantages and is an excellent choice for both rural and urban installations for a variety of reasons.

If you live in the city you may not have as much outside space and what you do have, you don’t want overwhelmed by a large, unattractive water tank. Even if you live in a rural location and have more room outdoors, an over ground tank can be a real eyesore and ruin a beautiful panorama.

Underground concrete tanks have the benefit of being completely hidden from view whilst still providing the same practical functions. If you’re short on space it doesn’t matter as they’re strong enough to be situated beneath a drive, path or garden area and don’t need to be completely isolated away from foot traffic. This provides a much greater scope to choose the size tank you really want rather than being confined by physical dimensions over ground.

If you’re concerned about the environmental impact, concrete is an excellent option as it’s a green choice for water tanks. And because there are no chemicals added, and there are no metal or plastic by-products, the water from the tank won’t be tainted in any way, or taste unpleasant.

Being underground means it’s always cool, and in turn, this eradicates the growth of algae. This results in much better quality of water from the tank and prevents your pump and valves from being clogged up and damaged by algae growth.

Construction methods and legal compliance

Craning in TankHaving an underground concrete water tank isn’t as simple as just placing a butt in your back yard as there’s lengthy compliance and legal requirements that have to be fulfilled in order for the installation to be lawful.

Under the Building Code of Australia water tanks are classed as structures and dealt with under section 10b and must therefore comply with the usual building regulation criteria.

Tanks that are set into the ground must be a certain distance from wastewater treatments, complying with AS/NZS 1547, which stipulates the horizontal space that must lie between them.

Tanks made of polyethylene that are situated above ground must comply with AS/NZS 4766 but any that doesn’t fall under this piece of legislation, such as underground tanks, must still be considered to be of a structurally sound nature and waterproof.

AS/NZS 1546.1 and AS/NZS 4766 can be used to assess whether these criteria have been fulfilled with this type of inspection being performed by a structural engineer.

Any products or materials that are intended to connect to the water supply must meet the standards set out by the National Plumbing Products Certification Scheme, and be on the approved list as described in AS/NZS 5200. This required is specified within the Plumbing Code of Australia.

There are a number of other standards that rainwater tanks must comply with:

  • AS/NZS 1546.1 – onsite domestic wastewater units
  • AS/NZS 4020 – requiring any materials or products to be tested that will come into contact with drinking water
  • AS/NZS 3500 – drainage and plumbing
  • AS 5200.000 – further technical specifications for drainage and plumbing products
  • AS 5200.026 – further technical specifications regarding drainage and plumbing products for cold water storage tanks
  • AS 3735 – concrete structures retaining liquids

The installation process

Installing an underground concrete water tank begins with the creation of the unit at the factory, manufactured to the standards required for the individual site. In installations where additional strength is required, the weight bearing capacity of the water tank can be increased.

300mm of earth can be placed on the top of standard tanks but lids can be manufactured to withstand greater loads of up to 2 metres of earth. Concrete slabs of up to 200mm thick can also be laid on top of the tanks.

Concrete Tank Installation GuideOne of the biggest disruptions during the installation process, and one that may make homeowners veer towards an above ground tank initially, is the excavation. To settle a tank sufficiently in the ground with no visibility and no likelihood of floating, it’s important that a sufficiently large hole is created. Conversely, it’s also important that the hole is not any larger than it needs to be in order to maintain the integrity of the earth structure surrounding the installation and helping to provide support.

Although this is a minor inconvenience in the immediate terms, once the water tank is in place and the earth replaced or removed, the long term benefits of opting for an underground tank far outweigh the negatives.

Ongoing use advice

Water collected into an underground concrete tank should be suitable for drinking water without any further filtration or boiling. However, the young, elderly or those with a compromised immune system may prefer to take precautions before consuming.

The most important thing is to monitor the surrounding environment to make sure there’s no way the water supply can become contaminated.

If there are any dangerous plants growing nearby, they should be kept pruned and clipped back. Gutters should be inspected regularly to make sure there are no small animal or bird carcasses, which can be a frequent problem.

Chlorinating the water isn’t normally required, and it’s not advised by the Environmental Health Committee in Australia as an essential measure, unless to remedy a specific problem. Using chlorine will only disinfect the water in the tank at that time; it won’t have any effect on new water that is added at a later date.

Essential maintenance and refurbishment

Because our concrete underground water tanks are manufactured using seamless moulds, there are no joins in our units. This means that there’s no vulnerable points that leaks could develop, creating a far more secure tank that’s built to last.

Nevertheless, it’s important to carry out periodic checks and maintenance to make sure your water tank stays in tip-top condition.

Epoxy Coated Underground Mine TanksCircular tanks typically produce more sediment than square or rectangular tanks because of the more limited movement but it’s important to check every type of tank regularly for sediment. You shouldn’t need to check the tank more frequently than every two years unless you suspect there’s excess sediment building up.

A qualified plumber should carry out a routine check on back flow prevention valves once every 12 months.

When the tank is first installed, there may be an unusual taste to the water but after flushing the tank through once, this should disappear. If at any time in the future the water develops an unusual taste you should check the tank and inlets for contamination and take corrective action as necessary.


If you haven’t used a water tank before, you may have some lingering questions about their use. Here are answers to some of the most common FAQS:

What can I use the water in my tank for?

The water collected in your tank can be a back-up for a wide variety of household and personal requirements, as well as helping to irrigate your garden. A supply of water for appliances such as the dishwasher and washing machine, toilet and bathroom can be obtained from your tank, and providing there are no known contaminants in the area, the water can also be safely drunk without any further filtration.

Can I move my above ground water tank underground?

The benefits of having an underground water tank are manifold so if you have an existing tank you may be wondering whether you can simply move it below the surface.

Having a tank that’s suitable for underground use is a complex affair as there’s a number of different factors to consider, plus the environmental conditions will be vastly different. For this reason the majority of manufacturers would say that their above ground tanks are not suitable for use in the ground.

In selected cases you may be able to partially bury an overground tank but by doing this, you wouldn’t get the full range of benefits that an underground tank offers. In addition, you would need to get an engineer to confirm whether the tank would be able to withstand the pressure and also hold its position without floating up.

How long will it take to collect water?

The rate at which your water tank fills up depends on the environmental and climatic conditions in your town and state. However, as a rough rule of thumb, rainfall at the rate of 1mm per hour, falling on one square metre of roof will produce one litre of water for the tank.

Are there any grants or rebates available?

The Australian government is very keen to encourage home owners to increase their usage of water tanks so there’s a range of incentives and rebates in place across Australia.

What’s available depends largely on where you are living with different schemes available in each part of the country.

The importance of having an additional supply of water is now so great that regulations stipulate that new homes must have one incorporated into the design.


An underground concrete water tank is an excellent investment and guarantees that your household will be able to generate its own water supply for decades without further interruption. Having access to a municipal water supply shouldn’t be any reason to delay getting your own water tank as it’s not just an environmentally friendly measure, but a step that could substantially reduce your water bill.

Call for a quote today to find out how you could take the next steps to protecting your household from any water shortages in the future, and being responsible for your own supply.

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