Rainwater Tank Types

Rainwater tanks are an integral part of a Rain Harvesting system.

When selecting a rainwater tank or tank to your house, you will be asked to choose between two broad categories: aboveground or underground.

As their name suggests, aboveground tanks have been installed, either next to your home, under it (for houses on stilts) or further away in your premises. An underground rainwater tank is set up completely underground or partially below ground. Like aboveground tanks, they can be installed alongside your house or farther away.

Your selection of aboveground or underground tanks may depend on several factors. Below, we explore the key differences between these options and the factors that might determine your pick one way or another.

Aboveground rainwater tanks

A popular option, aboveground tanks can be produced from concrete, metal (including steel), polyethylene (vinyl) or fibreglass. “Bladders” are another form of water storage device which may be installed aboveground in comparatively tight spaces.

If you can afford to, installing a rainwater tank is a good idea not only for permaculturists (although it does correspond very neatly with permaculture’s focus on recycling, using renewable energy and trying to maximize the number of functions they perform) but also for everyone. They are particularly beneficial in regions that experience periods of low rainfall and high temperatures, because they can store water from past rainy seasons for use as irrigation in case of a drought. Indeed, in one country, Australia, the installation of rainwater tanks is getting more and more popular, with more than a quarter of homeowners currently having one on their own property. There are some places — often those prone to drought in the summer — where new houses being constructed must incorporate a rainwater tank mandatory.

If you’re thinking about installing a rainwater tank on your website, there are a number of things to take into consideration. The size of your premises will be important, as will the amount of rainfall you get in your place, the dimensions of the roof where you will be reaping the water, along with the uses you would like to set the rainwater to. Another consideration is that the material that the tank is made from. Your choice will be linked to other things, such as use and space, but different substances have different properties that will have an effect on your choice.

  1. Concrete

    The huge mass of concrete tanks means that they are primarily installed underground. This is sometimes useful so as to conserve space at the garden, but will clearly need significant excavation in the first instance, which has the added effect of making them the most expensive kind of tank to install. Concrete tanks are more likely to be subject to planning restrictions than other, more light-weight tanks. If you put in a concrete tank, be aware that lime from the concrete can leach into the water, especially in fresh tanks. This can turn the water alkaline, which isn’t great for many plants. Using a liner for your concrete tank can prevent this, and remember to do pipe relining at least once in a few years to ensure steady water quality.

  1. Metallic

    Steel tanks have been the conventional alternative to a concrete tank, being an aboveground tank, even cheaper than concrete, and lighter, therefore, easier to install. Initially, metal tanks were made from stainless steel — significance steel sheets were coated with a coating of zinc — which allowed the steel to be soldered together, meaning tanks could be manufactured in different shapes and sizes. The issue with galvanized steel is they are prone to rust, especially if they’re used with aluminium or aluminium fittings and pipes. The rust from inside the tank which gets in the atmosphere is not harmful to plants (at least not unless it is in very large amounts ), but the rusting connected with galvanized steel tanks will eventually undermine the integrity of the tank, causing leaks and requiring a replacement. These days, manufacturers are using different metals, for example, aluminium to attempt to prevent rusting.

  1. Polyethylene

    The very low cost of polyethylene is just one reason why it’s now one of the most well-known choices of material for rainwater tanks. Polyethylene, or commonly known as poly rainwater tanks, are also very lightweight and so easy to transport and install. They might experience some rust if subjected to high levels of sunlight, but maybe not for several decades. Because they are manufactured by being molded around a central steel mould, they have a tendency to come in regular shapes — typically circular — and sizes (as producers don’t want the cost of producing a single mold for each client). This can be a downside if you have an irregular space as a location for your tank. 

  1. Bladder

    Should you have an irregular space, or a little space, for your tank, 1 option is to install a rainwater bladder. All these are made from a flexible membrane which develops when water enters the bladder, and contracts when liquid is siphoned off. Typically, rainwater bladders are installed in a rudimentary framework to stop movement and can be installed in the crawl space underneath your house in case you don’t have space in the garden (although remember to consult with your construction contractors as this may require some pipework to divert the feed out of the guttering beneath the house). They may also be used vertically, so can be set in a frame against a wall or fence. Bladders are, literally, the very flexible option for your rainwater tank, but do have the drawback of the very limited capacity of all of the options. However, in case you’ve got a small area, your water needs will be less than bigger places, and bladders may also be a feasible option if you want to use rainwater for household water needs and your dwelling is small or your household is few in number. 

Aboveground tanks are rather fast and simple to install, especially as you don’t need to excavate space for them. This makes them a comparatively low-cost choice for rainwater storage. Aboveground tanks are also simple to inspect for possible damage.

Underground rainwater tanks

Underground tanks are most commonly made from concrete or reinforced polyethylene (plastic). They are more expensive to set up than their aboveground counterparts since they require excavation along with the materials they’re made from need to be reinforced. 

The best benefit of underground rainwater tanks is their space-saving nature. They can be installed in smaller properties in which the size of your property would otherwise prohibit the use of a tank. Underground tanks are often installed underneath driveways and are a favourite option for new home developments. Some people also prefer underground tanks because they do not impact your house’s aesthetics. The downside is that because most of the components will be underground, it is easy to mistake the pipes to the ones that connect to the sewer lines, should there be a need to repair the drains.

The right tank to get

Your choice of aboveground or underground rainwater tank will be largely determined by your budget, accessible space and preferences.

Whatever you decide, make sure to complement your chosen tank/s with the appropriate equipment and processes to ensure your Rain Harvesting system gives you cleaner rainwater and lots of it.