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08 January 2026
Which type of water tank is best for the home?
The best type of water tank for a home in New Zealand depends on where the tank will sit on your property, how you plan to use the water, your budget, and how long you want the system to last. Concrete and polyethylene tanks remain the most cost effective options for most homes, while stainless steel is an excellent premium choice for longevity and sustainability when budget and access allow.
How to choose the best tank
Choosing the best water tank starts with how you plan to use the water and where you can physically locate the tank on your site. For many existing homes, the most practical choice is an above-ground polyethylene tank connected to roof catchments for garden use and non-potable indoor uses such as toilets and laundry.
Key decision factors for New Zealand homeowners include:
- Whether the tank is above ground or underground.
- Whether the water will be potable or non-potable.
- Local council consent and plumbing requirements.
- Site access and geotechnical constraints, such as earthquake risk.
Step 1: Clarify how you will use the water
New Zealand households typically use around 159 to 231 litres of water per person per day, depending on the season, with outdoor irrigation driving much of the summer increase. Diverting part of this demand to rainwater can significantly reduce pressure on council supplies, and studies show that using rain tanks for toilets, laundry and garden use can cut potable demand by up to 45 per cent in suitable homes.
Start by deciding how far you want the tank to offset this demand:
- Outdoor only use - simplest installation and often consent free for smaller tanks.
- Outdoor plus toilets and laundry - higher savings but requires compliant backflow protection and plumbing design.
- Whole of house including drinking water - requires treatment and strict compliance with potable standards and local council rules.
Step 2: Above ground vs underground
If you plan to install a tank underground, concrete remains the default choice because plastic tanks are generally limited to shallow burial and need specialist installation to avoid collapse. Underground tanks are popular on small urban sites because they preserve outdoor space and can double as structural elements such as driveways, patios or retaining walls when designed correctly.
For above-ground installations, polyethylene and stainless steel tanks dominate new residential projects due to easier transport, simpler foundations and faster installation compared with large precast concrete units that require crane access. In high earthquake zones, flexible connections and correct anchoring are essential, whichever material you choose.
Concrete water tanks
Concrete and ferro cement tanks are still widely used, especially where underground storage or high structural mass is an advantage. They are usually precast off-site and craned into place, which improves quality control but can limit their suitability on tight urban sections.
Advantages of concrete tanks
- Can be fully buried. This protects visual amenity and can free up surface space for landscaping or driveways when properly engineered.
- High thermal mass helps keep stored water cool, which reduces the risk of algae growth and helps stabilise water quality.
- Concrete slowly leaches lime, which can raise the pH of slightly acidic New Zealand rainwater and soften corrosive water, reducing long-term impacts on plumbing fixtures.
Limitations of concrete tanks
- Installation typically requires heavy lifting equipment and good vehicle access, so retrofitting into established residential sites can be complex and expensive.
- Concrete tanks can crack under ground movement or if not adequately supported and drained, which can be difficult and costly to repair once the tank is in service.
- They are usually more expensive upfront than polyethylene tanks and may require longer construction and consent lead times.
Concrete is often the strongest option when you need a large underground capacity or want the tank to integrate structurally with other elements of the building platform.
Polyethylene (plastic) water tanks (Poly Tanks)
Polyethylene tanks are the most common choice for above-ground residential rainwater storage in New Zealand and are often referred to as poly or plastic tanks. They are rotationally moulded in one piece without seams, which reduces the risk of leaks and allows a wide range of shapes, including slimline formats that fit narrow side yards.
Advantages of polyethylene tanks
- Lightweight and easy to manoeuvre on site, which makes them ideal for retrofits and properties with limited access for heavy machinery.
- Typically the lowest upfront cost per litre of storage among common residential options while still meeting food grade and potable water requirements when installed to relevant standards.
- Available in many colours and shapes, so you can better match cladding, fencing or landscape features and screen the tank from the street.
Limitations of polyethylene tanks
- Not usually designed for full burial, so visual integration relies on screening, fencing or careful placement around the house.
- More exposed to UV and heat, which can warm stored water and accelerate material ageing, especially in high solar gain locations if the tank is not UV stabilised or shaded.
- More vulnerable to mechanical damage from fire, sharp objects or impact, which can be an issue on rural or bush sites.
Modern high-quality poly tanks use UV stabilised resins, are typically designed for a 10 to 20 year service life, and can often be recycled at the end of life, which improves their sustainability profile.
Stainless steel water tanks
Stainless steel tanks occupy a premium space in the residential market, usually in smaller to medium capacities or where architectural appearance and longevity are key priorities. Constructed from corrugated stainless steel sheets, they visually echo traditional corrugated iron but offer superior corrosion resistance.
Advantages of stainless steel tanks
- High structural strength and excellent resistance to UV, temperature swings, and corrosion mean well-designed stainless steel tanks can last 20 to 50 years with appropriate maintenance.
- Tanks are relatively easy to repair through welding or mechanical patching, and the material retains scrap value, which supports recycling and reduces whole-of-life environmental impact.
- Smooth, inert internal surfaces support good water hygiene, which is valuable where water is used for potable purposes with appropriate treatment and filtration.
Limitations of stainless steel tanks
- Higher upfront cost per litre than both polyethylene and most concrete options, so total investment can be significant, particularly at larger volumes.
- Less commonly used for very large residential installations because material and fabrication costs escalate with volume compared with poly or concrete alternatives.
For homeowners looking for a long-term, low-maintenance and visually high-quality installation, stainless steel can deliver strong whole-of-life value even if the initial purchase price is higher.
Water Tank material comparison at a glance
| Factor | Concrete tank | Polyethylene tank | Stainless steel tank |
| Typical residential use | Large or underground storage | Above ground domestic rainwater | Premium small to medium storage |
| Usual installation position | Above or below ground | Above ground only | Above ground |
| Relative upfront cost | Medium to high | Lowest for most sizes | Highest per litre |
| Indicative lifespan | Long if well built and maintained | Around 10 to 20 years | Around 20 to 50 years |
| Structural / crane access | Requires heavy lifting and access | Light and easy to move | Moderate; lighter than concrete |
| Burial suitability | Well suited to full burial | Limited shallow burial only | Generally not buried |
| Sustainability profile | High mass; recyclable rubble | Recyclable plastics in many regions | Highly recyclable with scrap value |
Smart Water: why tank monitoring matters
Whatever material you choose, the real performance of a rainwater system depends on how effectively you manage levels and demand over time. New Zealand research highlights that outdoor use and seasonal peaks can significantly increase total water demand, so having accurate visibility of stored volume helps households avoid shortages and plan use through dry periods.
Smart Water tank level indicators provide continuous data on tank volume, consumption patterns and pressure. When connected to cloud services and in-home displays, this enables smarter irrigation scheduling, leakage detection and early warning when levels fall below critical thresholds. This type of monitoring helps homeowners maximise the value of their tank investment while supporting council objectives around water conservation and climate resilience.
At Smart Water, we have engineered the most advanced tank level indicator available that now offers full cloud connectivity.
Easy to install yourself, your Smart Water tank indicator provides you with all the information you need from our app or from one of our LCD displays. Find out how much water you consume on average from your tank, accurate pressure data and estimates on when your tank will run out of water based on current usage.
Find out more about our range of products or check out our FAQs for more information.
FAQs: choosing the best water tank for your home
Is rainwater collection legal for New Zealand homes?
Yes; across New Zealand many councils actively encourage rainwater collection for non-potable uses, although plumbing connections and backflow prevention must comply with the New Zealand Building Code and local bylaws.
Do I need consent to install a rainwater tank?
Small, stand-alone tanks used for garden watering are often exempt from building consent, while larger or plumbed-in systems usually require consent to ensure structural safety and protection of the public water supply. Always check your council guidance before committing to a specific tank size or location.
Which tank material is best for drinking water?
All three materials commonly used in New Zealand - concrete, polyethylene and stainless steel - can be suitable for potable water when built from approved materials and used with appropriate treatment and filtration. Poly and stainless steel tend to offer smoother internal surfaces and easier cleaning, while concrete can help stabilise pH in soft or acidic water.
How big should my water tank be?
Ideal capacity depends on roof area, local rainfall patterns, how many people live in the home, and whether water will be used indoors as well as outdoors. Smart Water provides detailed guidance on sizing and related topics in dedicated resources such as the rainwater beginner’s guide and tank sizing articles.
Why add a tank level indicator to an existing tank?
Without instrumentation it is difficult to know how quickly you are using stored water or to spot leaks and overflows, particularly on large or underground tanks. A Smart Water level indicator provides real time visibility of volume and trends which helps you manage demand through dry spells and protect pump and plumbing infrastructure.
Post first published 15 December 2021 and last updated 8 January 2026
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