29 January 2023

How long can you store rainwater for drinking?

As rainwater tanks become more and more popular throughout New Zealand, people are not just using their tanks to collect rainwater for non-potable uses such as watering the garden and washing the car. People are starting to turn to rainwater tanks as their primary water source for potable use around the house including washing, cooking and drinking.

One of the most common questions we see is people wondering how long you can store rainwater before it goes bad. The answer to this is not straightforward. It will completely depend on your rainwater tank set up and the way you collect your rainwater so the answer to the question can be anything from a few days to indefinitely.

How can I ensure the water in my tank is safe to drink?

Collecting and using rainwater can be a great way to conserve resources. Some people use rainwater for watering plants, cleaning, bathing, or drinking. However, it is important that the rainwater system is maintained properly, and the water quality is appropriate for the intended use.

According to the Centers for Disease Control and Prevention (CDC), “While useful for many things, rainwater is not as pure as you might think, so you cannot assume it is safe to drink. Rain can wash different types of contaminants into the water you collect (for example, bird poop on your roof could end up in your water barrel or tank). Rainwater can carry bacteria, parasites, viruses, and chemicals that could make you sick, and it has been linked to disease outbreaks.

It is therefore important to put in measures to prevent the contamination of your water and there are lots of options available when it comes to filtering and purifying the water that will be used for potable purposes.

Rainwater filtering and purifying solutions

If you are planning on using the rainwater you collect in your tank for potable purposes such as washing, cooking and drinking, it is important to put in place filtering and purifying solutions to ensure the water you are drinking is safe for human consumption.

There are a number of options when it comes to filtering and purifying the water that enters your home that has been collected in a rainwater tank. Here are some of the most common solutions, some of which can be used together to provide an extra layer of filtration for your water:

UV Filtration systems

A UV Filtration System treats unsafe water containing pathogens and bacteria with a germicidal ultraviolet light.  The UV wavelength scrambles the DNA of the live organisms, making them unable to reproduce and cause you to be ill.

A UV Filtration system can be used to treat the water of an entire house.  It does not filter out coarse debris, prefilters are necessary for that, but it does a great job at killing pathogens.

A UV Filtration system would be used in conjunction with other water filtering systems to ensure maximum protection.

Reverse Osmosis systems

Reverse Osmosis water filtration process is simple and straightforward. It is accomplished by water pressure pushing tap water through a semi-permeable membrane to remove contaminants from water. This is a process in which dissolved inorganic solids are removed from a solution. This process differs from standard filtration where impurities are collected within the filter media. The reverse osmosis process pushes water through a series of filters and ultimately the clean water goes to the holding tank, and the contaminants are flushed down the drain.

When household water pressure pushes water through the Reverse Osmosis membrane and additional filters, such as sediment or carbon filters, the impurities are filtered out and subsequently flushed down the drain.

Reverse Osmosis systems can be applied at two levels: point of entry (POE) which means that all water entering a house is filtered using reverse osmosis or point of use (POU) which can be applied to an individual sink within a house or even your fridge for example.

Ultra and Nanofiltration systems

Ultrafiltration is a form of filtration that uses membranes to separate different fluids or ions. Ultrafiltration is not as fine a filtration process as Nanofiltration, but it also does not require the same energy to perform the separation. Ultrafiltration uses membranes that are partially permeable to perform the separation, but the membrane pores are typically much larger than Nanofiltration membrane pores.

Both systems can be installed to filter the rainwater that enters your system, and they are typically deployed before a UV filtration system, capturing the coarse debris before it enters the system.

Storing rainwater for safe drinking

Historically in New Zealand, rainwater tanks have not been installed with UV filters or reverse osmosis systems, however, things are changing as people are becoming more aware of what they are putting into their bodies.

These new filtration processes are helping to keep Kiwis healthier, and they ensure that you can store water for longer in your water tanks without fear of contamination.

Of course, one of the best ways to ensure that water in your tank does not become contaminated is regular use. Whether this is for daily showering, watering the garden or washing the dishes, regular water use helps to ensure that fresh rainwater can be topped up in your tank.

This is particularly important for people who are collecting rainwater for use around the garden. Water barrels are notorious for going stagnant when not used on a regular basis and whilst they will typically get used daily during the dry summer months, winter can be a time to ensure you are using the water in your barrel to allow for the fresh collection of rainwater during those months.

Monitoring water quality

If you have a rainwater tank at home, it’s important to test the water in your tank on a regular basis. There are home kits that you can purchase to test your water quality at home, or you can send samples from your rainwater tank off for testing in a laboratory.

Carrying out regular testing of your water will provide you with the peace of mind you need if you are using the water you collect for potable purposes around the home.


Rainwater can be stored indefinitely if you have the right systems in place to ensure the water is safe for drinking once it leaves the tank and into your water system.

If you already have a tank installed or you are thinking of installing a tank, a great addition is a water level meter that will enable you to see how much water is in your tank at any time. These are particularly useful for large tanks that are used as the main source of water for a property, however, they can be installed on a wide range of water tanks.

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.