25 July 2024

How to filter rainwater

If you are thinking about installing a water tank, either as part of a new build project or retrospectively at an existing property, it’s important to understand the requirements when it comes to filtering rainwater.

No matter what you are using the collected rainwater for – whether it’s simply for watering the garden, washing the car, or whether you plan to connect your water tank to your home for potable purposes – the water you collect should be filtered before it enters your tank.

Whenever you store water, whether it’s in a simple rain barrel or a large tank to support the water requirements at your property, it’s important to ensure no debris enters the tank from the outset.

Potable vs non-potable water

Whilst the first line of defence is important no matter what you plan to use your collected rainwater for, there is a significant difference between the standards required for watering the garden versus drinking water.

Potable water – water you plan to drink, cook with or shower in – must be filtered from all debris and also pathogens and microbial pollutants before it is considered safe for consumption. Below, you can discover the different ways potable water can be filtered to ensure it is safe for drinking, cooking and bathing.

If you are simply using the water for non-potable purposes – which includes flushing the toilet or washing your clothes – then only a basic filtration system is necessary to ensure your water does not develop algae or bacterial growth.

Ways to filter rainwater

In this post, we are going to focus on the best ways to filter rainwater for potable purposes. These come on top of the basic filtration needed for all water tank solutions and are a necessary requirement if you plan on using the rainwater you harvest for drinking, cooking with or bathing in.

Ultraviolet (UV) light

One of the most popular options for rainwater filtration is the use of UV light. Once the rainwater has passed through the initial filtration system as the water enters the tank, the UV light will penetrate any living organisms’ cell wall, preventing their reproduction. This makes any organism that passes through the initial filtration harmless.

UV is a great solution as it has no impact on the chemical composition of the water, and also leaves no by-products in the water.

UV filtration helps to reduce the harmful pathogens in the rainwater you collect, making it safe for potable consumption. The UV filtration system is often the last filtration system that water passes before entering a property, ensuring that any tiny particles that may have been missed by other filtering methods are eliminated before the water leaves the tank.


There is a wide range of water filters that can be used to filter the rainwater you collect from your roof. The quality of the filters you use is measured by microns and the smallest size of particle they can filter. The smaller the micron size, the better the filter.

It is best to install this type of filter in a place that is easy to access so that it can be cleaned on a regular basis. All filters need cleaning periodically to ensure there is no build-up of debris that can stop the filter from working effectively.

Types of filters include:

·        Polypropylene and ceramic cartridge filters

·        Activated carbon filters

·        Micro/Ultrafiltration membrane filters

·        Reverse osmosis filters


Whilst this is not a way of filtering your water, it is a good way to ensure that the rainwater you collect is safe for drinking. Chlorine can be used as part of the water filtering and disinfection process and has been used for many years in public water systems.

Chlorine is highly effective against harmful bacteria, viruses and giardia and is considered a good option for keeping your water healthy.

Whilst chlorine is typically associated with keeping swimming pools and spas clean, it can be effectively used on drinking water. It is common for chlorine to be used in conjunction with other filtering methods to maximise its effectiveness. These include:

·        Filtering the water before the chlorine treatment to remove particulates or organics

·        Remove by-products of chlorine by employing another purification process such as reverse osmosis

To remove the smell of chlorine, you can also use an activated carbon filter or charcoal filter which is an eco-friendly solution.

Oxygenate the water

A great way to stop your water from going smelly is to use oxygenation. Whilst you do not want to disturb the particles that collect at the bottom of your water tank, using a calmed inlet ensures that you oxygenate the water from the bottom up, only oxygenating the water above the sediment.

Aeration helps to keep the water in your tank moving, lessening the stagnant, smelly water that is common if water sits for long periods of time.


A water tank is a great investment, especially as we start to encounter drier summers here in New Zealand. Collecting your own rainwater, no matter how you plan to use it, is a great way of saving money on your water bills, as well as contributing to a reduction in the amount of surface runoff which has serious environmental consequences.

At Smart Water, we are helping to facilitate growth in the water tank market by providing accurate ways to monitor the level of water in your tanks, no matter where you are. Our water tank monitoring system can be accessed from a desktop or wall-mounted LED display or from an app on your smartphone.

Find out more about our range of products or check out our FAQs for more information.