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Which Rainwater Tank is best for You?

Installing a rainwater tank is one great way of saving some of our precious water! Let’s look at some ideas that may help you…

If you already have a good idea of what kind of water tank you need, see the list of our shapes and sizes of poly and steel tanks and the advantages and disadvantages of each type of tank...

If you’d like some ideas and advice on things to look out for when collecting rainwater, then read on below.

These steps guide you through the choices you have and decisions you need to make. And we’re here to help at any point along the way, whether it’s all new to you or you just need a little detailed design help.

What size of tank do I need? Choosing the right size of tank
How much water can you save? Could I collect enough water to fill the tank?
Shapes and sizes of tank available Shapes, sizes and examples of what's available
Getting the most from your investment How to maximise use of your tank water
How much will it cost? Typical system costs
Planning & building requirements Some things you need to do
Maintenance What do you need to do to look after your tank
Our Service What we offer: Advice Design Installation Service

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What size rainwater tank do I need?

The best size for your home depends on how you plan to use your saved rainwater. Don’t worry about whether there’s enough rain to fill your tank – often the bigger problem is disposing of the excess water!

The Four Main Uses for Rainwater

You can do 4 main things with your rainwater tank:

These are listed below in order of increasing demand, tank size and cost.

1. Save rainwater to irrigate the garden with a bucket or hose

Comment Best size of tank

Connecting a raintank to a downpipe from your gutter to store water for when it gets hot in the summer is the simplest and lowest-cost option.

But the time of year when it rains and the tank fills isn’t generally the time of year that you need to water the plants. Your rainwater tank will be full for several months and then quickly emptied.

So whilst using a rainwater tank solely to water the garden is the lowest cost option, it’s also the least efficient in terms of cost recovery and maximizing usage.

As large as possible.

The cost per litre of water stored falls quickly as tanks get larger

Your options range from 300L up to 3000L in a slimline plastic tank (sometimes called an 'undereaves tank'), up to 7000L in a corrugated steel slimline tank or almost any size in a round tank

2. Store rainwater for drinking

Comment Best size of tank

Many people prefer the taste of rainwater over scheme water.

The Health Department does recommend mains water as the safest for drinking water and because you’ll otherwise miss out on the effects of fluoridation.

1000 to 2500L

Good filtration is important, to maximise the water quality in the tank and ensure it’s fit for use

3. Use tank water to reduce mains water use inside the home

Comment Best size of tank

An increasing number of new homes have the facility to connect the laundry and toilets to a rainwater tank . Using tank water to replace mains (scheme) water use through winter & spring will on average cut your total mains water use by 10-15% per year.

Minimum 3000L

But you can also supply your hot water system, and as that uses at least as much water as your washer and loo combined your annual savings could be increased to around 1/3 of total use. See Getting the most from your investment for more details

Around 5000L-6000L. Cost-effectiveness falls as the tank gets larger than this

Want to plumb rainwater into an existing house? It's relatively straightforward with an old house where the pipes run along the outside of the house, but is more effort when they're up in the ceiling. We can advise on how practical it would be

4. Replace mains water use inside your home

Comment Best size of tank

If you’re not on scheme water then an average household needs a water tank of minimum size 90kL just to provide water all-year inside the home. You'll need to harvest water off your entire roof too.

We have experience in designing and building these large systems for rural homes - ask us for more details

A tank of 130-160kL isn’t much larger or more expensive and will provide a reserve for dry years.

Two tanks are safer than one!

In general, look for the largest water tank that fits your space and budget. Larger tanks are not only more efficient but more cost-effective too. And round tanks are cheaper if you have the room to fit it into your garden.

See the Tank Sizes page for our full range of sizes and shapes

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How much water can I save?

Enough rainwater can be harvested from the average house downpipe to supply a 3000L tank connected to the toilets and laundry. Installations designed to maximise the use of rainwater will be more effective taking water from a couple of downpipes into a 5000L tank.

Did you know? Enough rain falls on the roof of an average Perth house roof to be self-sufficient in water – if only it could all be stored!

Many people have an issue finding a space next to a downpipe that’s large enough for the size of water tank they need. There are a couple of ways to solve this:

•  Run the downpipe along the wall to a better spot

Can look messy, and won’t work on all homes

•  Move the tank away from the wall – against the fence for example

Pipe can span across a path (much further and it’ll start to sag)

•  Run the pipe underground and then up into the tank

Works well and distance is not a problem but the pipe does remain ‘charged’ or full of water and the system must be carefully designed.

For a large tank draining most or all of the house roof this is generally the only practical option

How to get the most from your investment

For most people a rainwater tank is an investment in the future. As we don’t yet pay the true cost of water delivered to our door, it will take many years for a rainwater harvesting system to break even.

To make the most of your investment, plumb your rainwater tank so you can use the water inside your home. Yes, there are additional costs in doing this, but big advantages in terms of efficiency. Household appliances that use water frequently, such as your washing machine and toilets, will continually draw down the water level in the tank and create more storage capacity for the next rain shower. That's good! Because the winter rains keep refilling the tank, you will re-use the water tank capacity several times over a year.

A 3000L slimline tank may yield 25000L of water if supplying toilets and laundry. A 5000L tank could supply 75kL or more of water to toilets, laundry and hot water system – 15 times the capacity of the tank!

In terms of saving water:

Savings Installed Typical Installation Cost/litre


Collecting rainwater for the garden

1500L tank, no pump



Plumbing-in your laundry and toilets

3000L slimline tank, submersible pump



Also supplying your hot water system

6000L slimline & pump



Adding further tank capacity

e.g. another 3000L tank


”Going Large” ...putting in a larger rain tank

Is it a good idea to have a bigger tank? It depends a bit! If you're using the tank primarily for watering your garden, then the bigger the better. You'll be lucky if it refills through the dry summer, so the more water you've saved up by the time it gets hot, the better off you'll be.

If you have the space, remember that round tanks cost around 2/3 that of slimlines (due to the lower manufacturing cost)

In the metro area most rainwater tanks connected to the home will run out in October / November time - within a few weeks of the end of the winter rain – because of their limited capacity. Making your tank a little bigger (e.g., going from 6000L to 9000L) has minimal impact on the overall efficiency of the system. Unless you live on a rural block and have space for a large tank that will hold enough rainwater to last through most or all of the summer (e.g. 90kL or more) you should plan on your tank water only lasting 5-7 months per year.

What happens when the tank runs dry?

Through the dry part of the year your house will continue to be supplied with mains water. This is normally done through an automatic changeover device mounted on an outside wall which will supply tank water if available, without requiring any valves or taps to be turned on and off manually.

Using greywater indoors

It is possible to use greywater (the waste water from your showers or laundry) to flush toilets inside the home. You’ll need a Greywater Treatment System (GTS) to do this, which purifies the water sufficiently for it to be used safely inside the home. These systems are expensive to install, and need regular servicing thereafter. Unless water is in very short supply we don’t recommend use of a GTS.

For the most cost-effective water savings, plan on using rainwater inside your home, and greywater on your garden through a simple Diversion Device (GDD). See the Greywater Page for more info.

"Gareth did a great job. Very professional"

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How much will it cost?

What you pay for a system to be installed will vary depending on:

A pump will almost always be needed to get enough pressure to connect to household devices or use a hose

Other plumbing fittings will be needed including first flush devices, overflows and insect screens, and possibly other items such as backflow prevention

Some example costs would be :

1500L tank installed for garden irrigation From $1100
3000L slimline tank installed for garden irrigation From $1750
3000L tank plumbed into a new home From $3000
6000L tank supplying laundry, toilets and hot water system From $5500
5000L underground tank plumbed into new home From $7000

Planning and Building Requirements for Rainwater Tanks

A typical domestic-sized rainwater tank does not need approval from most councils. If the tank is against the fence line then a height limit of around 1.8m generally applies. We can advise on the specific requirements for your property.

Tanks must be connected to a domestic system by a licensed plumber to ensure that all regulations are met to ensure there’s no contamination of the public water supply. Creative Clearwater Solutions will take care of that for you as part of our installation service.

You can use tank water inside your home for anything you want. As a standard we follow Health Department guidance and suggest to clients not to plumb a tank into the kitchen supply if they have the choice of using mains water, but it's up to you whether you follow that advice.

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Tank Maintenance

Regular maintenance is an essential part of having a rainwater or greywater system. You must regularly check for overhanging branches, clean leaves and debris from your roof and ensure screens and filters are effective.

We provide a customised maintenance plan for you as part of our installation service, and can even do it for you if required.

Our Service

Creative Clearwater Solutions provide a complete service!

Creative Clearwater Solutions are an agent for many of the main tank suppliers. This means that we can get hold of the best solution for your specific needs – for example a particular width or depth of tank.

We are also a recommended installer for several of the largest manufacturers, with a lot of experience of delivering creative solutions to your water needs. See our installation galleries for more examples and selected case studies

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