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Slimline Water Tanks

Picking the right water tank for your home is not an easy task. It’s not just about choosing the right size, but also about finding enough space to set the tank up in the right location.

Water tanks can be round, rectangular, made from flexible bladders, or “slimline.” Slimline water tanks are one of the best options in urban or metro areas where lack of space is a big constraint, and customers don’t have the space to fit larger footprint tanks on their blocks.

In this article, we will talk about the various aspects of slimline water storage tanks to help you decide if they are the best option for your home.

What are Slimline Water Tanks? 

As the name suggests, the slimline design stands for a slim water tank. They have an oblong shape with a narrow profile that can fit small narrow spaces. While they are space-saving, they can also hold a large volume of water. These tanks are available in sizes ranging from 1000 litres to above 8000 litres.

The width of a slimline tank can be as narrow as 400 mm. While the height can be around 4000 mm. Quite simply, the design allows you to store a large volume of water in a small footprint. In case you need a higher capacity, you can also choose a modular arrangement. Here, two slimline tanks are connected end to end.

Since they have a narrow width, slim rainwater tanks are popular in suburban areas around Melbourne and Sydney. They are equally effective for houses built over small areas. A slim water tank is also great in areas where delivering a round tank is difficult. In fact, these tanks can also be custom-built to fit through narrow entry points.

Note, the average site area of Australian houses has come down in the past decade. We only anticipate this trend to continue, as land prices become more and more expensive, and tiny homes and modular homes become more popular. This is one primary reason behind the increasing popularity of slimline tanks as a space-saving option.

How Does a Slimline Water Tank Work? 

Slimline water tanks work like any other water tank. Their unique shape does not make them lack quality or performance. 

These tanks are generally made from polyethylene and have a rotomoulded construction. Stainless steel tanks are also available in slimline configurations. Since concrete lacks lightweight flexibility, it’s generally not usually used for these tanks.

Slimline water tanks can be used with any typical rainwater harvesting system. Rainwater collected on the roof or the catchment area flows into the tank through the guttering or pipes. The water is pumped to your home through the pipes and is passed through filters as needed.

Generally, a slimline rainwater tank usually comes with an inlet filter or screen that prevents debris and insects from entering the tank. It also has an overflow line at the top to allow the excess water to flow out. An outlet line with a fitting is also connected with the tank. You can specify the fitting as per your requirement.

Keep in mind, tank suppliers do not typically provide outlet line filters, pumps or other accessories with the tank. You need to select them on your own.

Who Uses a Slim Water Tank? Why Have One? 

Obviously, the primary purpose of choosing a slimline tank is to save space. If you have sufficient space, you can choose a rainwater tank of any shape. But slim tanks are great for properties with limited spaces.

Another advantage of slimline rainwater tanks is they are available in a wide range of colours. They can even be matched with the colour scheme of your home. That allows these tanks to blend with the surroundings.

This makes them an aesthetic choice for modern, contemporary, beachside, or rustic constructions. Many homeowners choose a slimline tank for its unique look. Besides, they can be easily set up along the wall or the fence line.

However, when you are looking for the maximum water capacity, the round water tanks are the best options, They are available for sizes above 20,000 litres and are ideal for large homes.

In addition, round tanks are self-supporting. A slimline water tank above 1.6 meters in height with a narrow base can topple over during severe weather conditions. So they need the right installation with a level concrete base preparation. Ideally, the concrete base should be at least 100mm thick and 150 mm wider than the tank footprint.

In order to prevent structural deformation, large capacity slimline rainwater tanks need internal and external baffles. Without the support, they are likely to get deformed from the water pressure. Such conditions often result in the bulging of the tank walls.

Due to these reasons, the price of slimline tanks is higher than standard round or rectangular water tanks. Even so, the advantages they offer in terms of space, outweigh the cons.

Typical Issues or Concerns of Traditional Rainwater Collection Tanks 

No matter what the shape of a water tank is, it is not going to provide you with the best service if it’s under-maintained. Remember, it is better to inspect the tank at regular intervals and fix small issues at the earliest. Repairing the tank if it suddenly fails can be difficult and more expensive.

Here are some common problems associated with rainwater collection tanks 

  • Tipping or settling of the water tank is a problem that occurs due to uneven stress distribution or a faulty installation. Large capacity water tanks are extremely heavy and any installation error or the lack of a level base can lead to imbalance. This may cause the tank to settle unevenly or tilt in one direction.
  • A common problem with rainwater collection tanks is a strange smell inside the tank. In most cases, this is due to the growth of algae inside the tank. Using a gutter mesh or chlorinating the water can reduce this problem.
  • Maintenance and inspection can be an issue with slim water tanks. Even with the use of a filter, sediment deposition at the bottom will happen. Reaching inside the tank is necessary for periodic cleaning of the sediments. The narrow shape of slimline tanks makes it difficult for a person to use the power tools required for cleaning.
  • In some cases, the tank inlet screen or pipe can get blocked. This can prevent the water from entering the tank.  Cleaning out the blocking material is the best way to solve the problem.
  • Another common issue is leaking around the tank fittings or a damaged pipe. If a flexible connector is not used at the connection points, the pipes can get bent or damaged in high-stress situations.

Choosing the Right Slim Rainwater Tank

To start with, check the rules regarding rainwater tank requirements for your local council.

Beyond that, there are a few factors that you need to keep in mind while choosing a rainwater tank. Let’s take a quick look at them.

Storage Capacity

This is the most important aspect of determining the size of the tank you need. Consider the number of persons in the house and the water consumption rate for determining the size.

The other important step is to find out the amount of annual rainfall and estimating your rainwater harvesting capacity. If the rainfall is distributed throughout the year, a tank with a smaller size should be good enough. You can take the help of tank sizing software to determine the size.

Tank Material

The three main materials for slim rainwater tanks are concrete, polyethylene, and stainless steel. Since concrete tanks are heavy, they are not the best option for most users. Polyethylene tanks are lighter and do not corrode easily. They also come with warranties that can be as high as 20 years.

Stainless steel tanks are extremely strong and do not deform easily. However, they need more maintenance and are prone to corrosion.


If you have already decided to go with a slimline tank, you need to decide on its location. A sturdy, level surface beside a wall or a fence should be a good spot. Also, consider the length of the downpipe and whether you need to use an aboveground or underground pipe system.


The price of the tank will depend on the size that you choose and also on the material. Compare the price of polyethylene and stainless steel tanks to find out what suits your budget. Generally, a tank with a higher price should come with an extended warranty. Don’t forget to add up the costs related to transport and installation.

Slimline Water Tank Case Studies

Since Australia is one of the countries in the world with the highest rate of water consumption, rainwater tanks play a significant role in water conservation. In fact, a study conducted on rainwater tanks of various capacities in Sydney has shown significant cost savings of the process for the owners.

Besides, a recent study has indicated that householders value slimline water tanks more than traditional round tanks. This is due to the fact that slim tanks have a less obstructive design and require less space for installation.

According to the study, the average expense buyers are ready to make for a round polyethylene tank of 4400-liter capacity is $2300. However, such buyers are ready to pay an additional amount of  $770 for slimline tanks.

To sum up, there is a clear indication that Australians are ready to pick slimline water storage tanks over traditional water tanks.


All in all, slimline water tanks are the best space-saving solution for setting up a rainwater harvesting system. Unless you are looking for a tank with ultra high capacity, choosing a slimline tank can be an excellent option.