How to choose the right water tank for your property

Choosing a water tank is straightforward once you understand the four decisions that matter. They are: what you will use it for, how much capacity you need, which shape suits your site, and what material makes sense. This guide walks you through each one, so you arrive at the right tank for your property without wasting time on options that will not work for your space, budget or aesthetic.

1. What are you storing the water for?

This shapes everything else, because different uses have different requirements for tank size, material, and how the plumbing connects.

Drinking water and household use

If you are in rural location or supplementing / replacing mains supply for potable use, your tank needs to meet AS/NZS 4020 standards for drinking water storage. This standard governs materials in contact with water intended for human consumption. Our corrugated steel water tanks use AQUAPLATE steel which is manufactured specifically for use in water tanks and has a food-grade lining integrated into the material which meets this standard. Not all suppliers can say the same, so it is worth confirming compliance with any supplier.

Garden and irrigation supply

Lower-specification requirements than potable storage, but you still want a tank that will not leach chemicals or degrade over time. Our above-ground steel water tanks are best in class. They are non-combustible, UV-stable, and do not require special treatment for irrigation water.

Stormwater retention and detention

If you are managing stormwater runoff on a residential or commercial site, the requirements are different again. Retention tanks store water for reuse; detention tanks temporarily hold stormwater and release it slowly to prevent overwhelming the drainage system. If your council requires stormwater management as part of a building consent, you will need to specify the right tank type and capacity to meet the requirements.

2. How much capacity do you need?

Capacity is measured in litres and depends on what you are using the tank for and how much roof catchment area you have.

For most households using rainwater to supplement garden irrigation or non-potable household use, tanks in the 600 to 5,000 litre range are common. If you are aiming for significant household supply or you’re on a property relying primarily on collected rainwater, 10,000 to 40,000 litres or more is more appropriate depending on the number of people in the household, rainfall and access to water delivery services etc.

A rough starting point: a 100m² roof catchment in a region with average rainfall (around 1,200mm, in line with NIWA data for Auckland and other main centres) per year can collect approximately 100,000 litres annually, far more than most households will store at any one time. What you are sizing for is the gap between dry periods, not annual total rainfall.

Three things inform capacity more than any rule of thumb:

Your roof catchment area: larger roof, more potential collection
Your local rainfall pattern: how long your dry periods typically are
Your intended use: daily household use requires more storage than garden-only use

3. Which tank shape suits your site?

Shape is primarily a space decision. Different profiles suit different site constraints, and choosing the wrong shape often means difficult installation, wasted space, or a tank that simply will not fit where you need it.

Slimline water tanks

Designed for narrow spaces, alongside a house, against a fence, or in areas with restricted access. Our Slimline water tanks have a long, narrow footprint, which means they can hold significant volume without taking up much width. Capacity ranges from 500 to our market-leading 10,000 litre tanks. If you are in an urban environment with a standard section, a Slimline tank is often the most practical choice.

Modline water tanks

A flat-ended design with a modern profile that suits contemporary architecture. The smaller footprint (due to the flat ends and the reduction of volume lost on a tank of the same size with rounded ends) makes them useful where both width and length matter. Our Modline water tanks are available from 770 to 10,000 litres.

Square water tanks

The smallest footprint of our above-ground range for equivalent capacity, square water tanks are useful where both width and length are constrained. Available from 530 to 10,000 litres.

Round water tanks

The traditional water tank shape, popular on commercial, lifestyle or rural or semi-rural properties where space optimisation isn’t a key requirement. Round tanks‘ curved profile takes up more of the site footprint than a flat-sided tank, so they suit sites with room to spare rather than tight urban sections. Available from 550 to 24,500 litres in above-ground corrugated steel.

Underground water tanks

A great option when you have no practical above-ground space, or when you want a completely concealed solution. The Li-Lo flat-plastic tanks we distribute require around 80% less excavation than a traditional cylindrical underground tank, and the ribbed base self-anchors without concrete ballast. They can be installed under a lawn, garden, or driveway. The cast iron cover (Class B) and cement support ring are suitable for installation in light traffic areas (max. total load 3.5 tonne). Available in 1,500, 3,000, and 5,000 litre sizes.

4. Which material: steel, plastic or concrete?

For above-ground water tanks, the practical choice is between corrugated steel, plastic (polyethylene) and concrete. All three are widely used and suit different priorities.

Corrugated steel water tanks

Our corrugated steel water tanks are made with AQUAPLATE® steel, meeting AS/NZS 4020 for drinking water storage, and are backed by a 20-year corrosion warranty and 10-year construction warranty with no pro rata reduction. They are custom made to your site’s dimensions, non-combustible, and hold their shape without bulging or bowing as they fill. For most urban properties, particularly where the tank will be visible or positioned close to a dwelling, steel is generally the better long-term choice.

Plastic (poly) water tanks

Plastic tanks can be cheaper upfront than steel, though this is mainly true of round tanks; for slimline and modline tanks, the shapes most urban and residential sites use, steel is often equivalent to or cheaper than plastic even at smaller sizes. Weight is not the advantage it is sometimes assumed to be either; steel is often the lighter option of the two at equivalent capacity. Plastic tanks come in fixed shapes and sizes, have setback requirements from buildings and boundaries, and can become brittle with sustained UV exposure over time. Round plastic tanks remain a worthwhile option for basic rural storage where price is the main consideration.

Concrete water tanks

Concrete is a third material used for water storage in New Zealand, though it shows up far more often in large in-ground and commercial installations than in everyday household setups. It is heavy, effectively permanent once placed, and generally the most involved and highest-cost option for an equivalent capacity, so it tends to make sense at large scale.

5. Other things worth knowing before you buy

Fire resistance

Corrugated steel is a non-combustible material. This matters for where you can legally position the tank on your property. Our steel water tanks can be placed beside dwellings or against boundary lines, which is often not possible with plastic tanks. Check your local council rules and the NZ Building Code requirements for your specific situation.

Warranty

Our above-ground steel water tanks are backed by a 20-year corrosion warranty and a 10-year construction warranty, with no pro rata reduction over the term. That means the cover doesn’t shrink year on year the way many plastic tank warranties do.

Connection placement

One of the advantages of our steel water tanks is that you specify exactly where you want the inlet, outlet, and overflow connections positioned before manufacture. The tank arrives on-site with all fittings installed and ready to connect, with minimal plumbing work required. Off-the-shelf tanks have fixed connection positions that may not suit your site, adding cost and complexity at installation.

Base preparation

All above-ground water tanks need to be installed on a firm, stable, level base with no overhang. A concrete pad is standard; pavers or an engineered timber platform is also suitable. Our tank base preparation guide covers the requirements in detail.

Delivery and access

We deliver to metropolitan Auckland at no charge and can arrange nationwide delivery. Larger tanks require adequate site access for delivery vehicles.

Lead time

Standard lead time for above-ground steel water tanks is five to six weeks from order, excluding delivery. Specifying a non-standard size does not extend this.

6. Where to go from here

If you know what you are looking for, browse a selection of our most popular above ground corrugated steel water tanks. If you need some guidance, alternative sizes or a custom made tank, talk to our team. We’ve been making tanks since 2008 and can usually work out the right solution for your needs in a short conversation.

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