I have owned a few rainwater tanks on my property, and choosing the right one can certainly be a confusing task. And what is most difficult is finding a non-biased view and navigating all of the information from suppliers on the internet. What I hope to do with this article is break down the facts and give you the pros and cons of the various tank materials and features so that you can make an informed decision.
See our reference table below which will give you an initial idea of the basic options. Then read on to find out more details so that you are equipped to make a decision as to which option is best for you. From there you’ll be prepared to speak to suppliers and get some costing.
| Common Types | Cost | Approximate Life | Ease of Installation |
| Steel (Corrugated) | Low | 20 years | Easy |
| Steel (Bolted/Liner) | Moderate | 30 years | Moderate |
| Stainless Steel | High | 40 years | Easy |
| Polyethylene | Low | 20 years | Easy |
| Bladder | Low | 10 years | Easy |
| Fiberglass | Moderate | 30 years | Moderate |
| Concrete | High | 50+ years | Complex |
Table of Contents
Types of Rainwater Tanks: Making the Right Choice
When designing your rainwater harvesting system, you have many tank options. Tanks come in various materials, shapes, sizes, and colors.
The first thing you’ll normally want to do is to determine the right size tank to meet your needs. This should consider the roof area (and therefore how much rainwater you can collect), and also your water usage. Have a look at our calculator on this here: Rooftop Rainwater Harvesting Calculator.
The main material options are discussed below.
Steel Rainwater Tanks
Steel tanks are a good choice in many applications, particularly if there is a local supplier that can manufacture a tank to your size requirements. Suppliers will probably have a few size options which they prefer to sell, and which will be a little cheaper. These will be the sizes that optimize material usage. However, given they are fabricated you should be able to request any size you like. I even have a slimline steel tank which was designed specifically to fit under the eaves of my shed to capture rainwater from the guttering. In this way, steel tanks can be more flexible than other options.
Steel tanks are resilient and if installed correctly, will last many years. There are a few steel options to consider, which will have varying costs and service life:
- Corrugated steel. These can be galvanized, or enamel coated such as colorbond, providing resilience from rust. For drinking water, the manufacturer may install a coating on the inside to make it safe. In most places, these are readily available and will give decades of service with no problem. They are also on the lower end of the cost spectrum and reasonably easy to install. Corrugated steel tanks are a great option for many rainwater harvesting systems. If you are thinking this way, it’s always worth doing a cost comparison from the supplier in your local area against poly tank options.
- Bolted steel. These are usually supplied with an antimicrobial liner, making them perfectly safe for storing drinking water. Larger steel tanks are usually bolted steel as they can be built taller than corrugated steel tanks. They are often used by utilities, where millions of liters must be stored. You can also get glass-fussed to steel tanks which are ideal for drinking water, but these are not common for small-scale home systems.
- Stainless steel. These are also less common in home systems and are more likely to be found in industrial applications. They are higher cost but provide exceptional service life. They are also likely to be fabricated for you, so you could specify precise dimensions and capacity if that is your priority.
Plastic (Poly) Rainwater Tanks
Plastic or poly tanks are lightweight, cost-effective, and easy to install. Built from moulded polyethylene, poly tanks are also tough and should give you a good service life. They are available in various sizes, although you will need to stick to the size options available since the manufacturer will have a certain set of mould forms. That said, they do come in many sizes and there are even slimline options. Polyethylene is an excellent material for drinking water. Many potable water pipelines are now built with polyethylene.
Poly tanks are a great option for many rainwater harvesting systems. If you are thinking this way, it’s always worth doing a cost comparison from the supplier in your local area against any corrugated steel options that are available.
Fibreglass Rainwater Tanks
Fibreglass tanks are another good option, although less popular for rainwater harvesting systems. They are common in industry.
Fibreglass tanks can be bolted together in sections or come as single units. They are strong, lightweight, non-corrosive and non-combustible. They can be a good option if there is a fire risk. You’ll also get a very good life from a fiberglass tank that is installed correctly. Perhaps around 30 years or more.
Being somewhat brittle, they are prone to cracking if not looked after, or if things fall on them. Something to keep in mind.
Concrete Rainwater Tanks
Concrete tanks are expensive but give excellent service life. They are also highly durable if built well and they are safe to use for drinking water. Concrete tanks can be built to any size or shape, but you’ll want to ensure your tank is carefully designed and constructed so that it is structurally sound. They can store large amounts of water and hence are common for municipal applications where large capacity, long service life tanks are required.
Design for concrete tanks, and the construction of them, is beyond the scope of this article. There are some great resources available for building them, although for most people it is advisable to bring in a specialist contractor who will have the correct formwork and designs to give the result you are after.
Special Types of Rainwater Tanks and Their Advantages
There are also some special types of rainwater tanks, tailored to meet specific needs or constraints.
Small and Compact Rainwater Tanks for Small Spaces
For homeowners with limited space, slimline or small round tanks can be an ideal choice. Slimline and other compact tanks are available on the market to fit neatly into any small area. They will only hold small volumes of water, but you can connect a few of them together if needed.
They can be a great option for apartment living where you have access to a room and a small outdoor area.
They can also be good for fitting under stairs, below decks, under eaves, or other convenient and out-of-the-way places.
Underground Rainwater Tanks
For those who prefer discretion or want to save space, underground water storage tanks are an excellent option. Their installation will be more complex and costly than aboveground tanks, but the benefits in some situations may be worth it.
These are typically concrete and designed bespoke for the situation, however, there are poly tanks that can be installed underground also.
Being underground, you’ll of course also need to think about how you will pump the water out for use. pipework and pumping will need to be part of your design.
Bladder Tanks
Bladder tanks are typically made from a flexible, but heavy-duty PVC material. They may have a steel structure supporting them, or they may lay on the ground. They are low-cost, easy to install, and can be quite versatile. Many people use them under their house or decking where there is limited height space. They are unlikely to give you the service life that other materials will, but they can be a good option in some situations.
Key Points to Consider When Choosing a Rainwater Tank
Beyond tank materials and types, there are other factors to consider to ensure you get the best outcome for your situation.
Foundations
Often overlooked, but it is essential for the life and performance of a tank to construct appropriate foundations. For small tanks, this might be as simple as leveling and compacting the ground and laying some fine gravel or sand. For larger tanks, you might need a concrete ring beam to be designed around the edge of the tank.
The foundations you require will depend on the ground conditions and manufacturer’s requirements for the tank you have chosen.
Wildfire Zones: Which Rainwater Tanks Are Best
If a fire is extreme, any tank will be damaged or destroyed. However, the risk is reduced by selecting the right materials.
In wildfire-prone areas, choose tanks with fire-resistant materials such as steel or concrete. Fiberglass may also be an option. Concrete will likely perform the best in a fire.
There are also glues and seals used in steel and fiberglass tanks that may not withstand high temperatures.
Also, remember that the plumbing connected to the tank may not be fire-resistant and you should think about measures you can take to reduce the risk to pipework and fittings.
Tank Maintenance: Dealing with Algae and Proper Cleaning
Choose a tank with no light penetration, either through openings in the top, or light materials. Light may cause growth of algae which you’ll want to discourage.
Positioning of your tank, and the outlet valving arrangement, should allow you to flush (or scour) the tank out periodically. Make sure there is somewhere safe to discharge this water to, without undermining the tank foundations.
Tank Installation: Do-it-Yourself or Hire a Professional
If you are installing a lightweight tank, doing it yourself may be an option. You’ll need to prepare the area and ensure there is an adequate foundation. As we’ve discussed, larger tanks will require concrete ringbeams which must be designed by an engineer for the load of the tank. Make sure the surface that the tank sits on is clean and free of sharp stones or any other material that may damage the underside of the tank. Carefully position the tank, orientating the outlet and inlet as required for the connecting pipework. Depending on the local requirements, you may need to engage a registered plumber to install the plumbing.
Installing a tank yourself may save money. However, you must understand the structural and plumbing requirements and it could cost you more in the long run, if not done correctly. For complex tank types like underground, concrete, or large-sized tanks, consider engaging a professional installation service. The tank supplier may provide that service or advise on options for contractors in your area.
Legal Requirements and Guidelines for Rainwater Tanks
In some areas, there are laws about rainwater harvesting, so always understand and follow these requirements before proceeding with your project. For example:
- It may be mandatory to engage a registered plumber to do the work.
- There may be restrictions on the use of certain tank types for drinking water.
- There may be requirements imposed by the local water utility preventing the connection of a rainwater tank to a system that is also connected to the mains water (or they may require backflow prevention valves etc.).
A Final Thought
In conclusion, knowing the options is important for you to choose the right rainwater tank for your situation. The best tank for you will depend on your needs, the available space, the trade-off you wish to make between cost and service life, and other factors.
The decision may also depend on what is available in your area. The size of water tanks can make them expensive to ship so you might need to accept what you can get around the corner. But being across the various pros and cons of the available options will ensure you can have an informed discussion with the supplier.
Good luck with your rainwater harvesting journey!
FAQs
Q: What factors should I consider while choosing the right rainwater tank?
A: Choosing the right rainwater tank requires you to consider several things. Firstly, you’ll need to determine the right size to meet your needs. This should consider the roof area (and therefore how much rainwater you can collect), and also your water usage. Have a look at our calculator on this here: Rooftop Rainwater Harvesting Calculator.
It’s also a good idea to think about where you’ll be locating the tank and the space and height constraints.
Also, think about the trade-off between cost and durability. For example, a concrete tank will be very expensive but last a very long time. A poly tank will be much cheaper but give you less service life.
Q: What are the benefits of using a rainwater harvesting tank?
A: Using a rainwater harvesting tank can significantly reduce your water bill. By collecting and storing stormwater, you can use it for purposes such as gardening, toilet flushing, washing clothes, and even drinking, if you’ve assessed the health risk (see our article on this here: Can you collect rainwater for drinking? What you need to know). Rainwater harvesting is sustainable and can help in reducing your reliance on mains water.
Q: How do I determine the right tank size for water storage?
A: The right tank size for your water storage depends on your intended water usage from the tank and the size of the roof area used for rainwater harvesting. Have a look at our calculator on this here: Rooftop Rainwater Harvesting Calculator.
Q: Do rainwater tanks come in different designs?
A: Yes, rainwater tanks come in a variety of designs to suit different space and style preferences. If you’re short on space, slimline tanks or underground tanks may be worth considering as they can be made bespoke to your needs. Poly or enamel steel tanks are available in a range of colors to suit your property’s aesthetic.
Q: What are the benefits of installing a slimline tank?
A: A slimline tank is a great option if you’re short on space. This type of water tank is narrow and elongated to fit into tight spaces. They are great for putting against walls, and under house eaves for collecting rainwater from roof guttering. Despite their slim nature, they can still be designed to hold a significant amount of water, making them a practical and efficient solution.
Q: What are the pros and cons of using a metal storage tank?
A: Metal storage tanks, typically made from steel, are durable and can be fabricated to suit your needs. There are a variety of materials and designs available on the market. Stainless steel; corrugated (enable coated or galvanized); bolted steel etc.
Whilst you should expect many decades of service life, they can be prone to corrosion over time. Manufacturers apply corrosion-resistant coatings to mitigate this issue.
Q: Can I install underground water storage tanks?
A: Yes, installing an underground water storage tank is an option. These are typically concrete but can be polyethylene. They are ideal when you want to save space or maintain your property’s aesthetics as they are essentially hidden. However, installation is complex and typically involves higher costs and effort.
Q: What material is best for a water tank?
A: The ‘best’ material for your water tank depends on your specific requirements and preferences. Polyethylene, or plastic tanks, are generally lighter, easier to install, and come in a variety of shapes and sizes. Steel tanks can be highly durable. Concrete tanks will give you the greatest service life but will be the most costly and complex to design and build.
