29 January 2023

Is rainwater clean?

With so many households and businesses choosing to collect the rainwater that falls from the sky in rainwater tanks, it is important to understand more about the process of collecting rainwater and how to ensure that the water you are collecting is safe for drinking or even for non-potable tasks such as washing the car or watering the garden.

All rainwater is not created equal. There are a number of factors that determine the quality and cleanliness of the water that falls from the sky so when we are answering the question “is rainwater clean?”, there are a number of factors that we need to take into consideration.

As rain falls from the sky, it absorbs pollution, pollen, mould, and other contaminants including dust and low levels of bacteria. If these are not filtered out of your rainwater before you use it, especially for drinking.

Is rainwater 100% clean?

Despite the potential for rainwater to collect pollutants on its way to earth, it is in fact one of the purest forms of water as it doesn’t have any dissolved impurities. As rainwater hits the ground, it then starts to dissolve impurities as it makes its way into waterways including rivers, lakes, underground bores, and aquifers.

Collecting rainwater in a tank, however, also leads to potential pollutants being absorbed by the natural rainwater as it falls onto your roof and is then diverted into your tank via the downpipes that connect your gutters.

Your roof can contain all sorts of debris, bacteria and residues that can contaminate the water you collect in your tank. It is important to filter these impurities before they enter the tank, otherwise, you can end up with debris in your water including:

·        Leaves, soil, and other debris

·        Bird, possum, and other animal droppings

·        Heavy metals such as lead from your roof or roof paint

·        Ash and chemical residues from local spraying or vehicle emissions

Keeping your rainwater pure

Whilst you might not be able to keep the rainwater you collect as pure as when it falls from the sky, there is plenty you can do to keep your water as pure as possible and safe for use, either for potable purposes or for watering the garden or washing the car.

One of the best ways to maintain the quality of the water in your tank is to prevent contamination from the outset. If you are simply using the water to water the garden or clean the car, there are some basic things you can do to prevent contamination including:

·        Use a screen over the tank’s inlet pipe to keep out insects, birds, and animals.

·        Install gutter screens to prevent debris from entering the gutter but don’t stop the water flow. These screens should be cleaned on a regular basis.

·        Ensure the tank is tightly covered.

·        Use a ‘first flush diverter’ – a simple device that fits onto your downpipe or tank inlet and prevents the initial flow of contaminant-laden water from the roof from entering the tank when it rains.

If you plan on using the rainwater you collect for drinking, cooking, and bathing, you will need to treat and purify that water on top of the above measures. There are a few options available when it comes to purifying water and these will all add costs to your installation and include:

·        Adding chlorine

·        Use a very fine inline filter or purifier

·        Boil the water for one minute

·        Ultraviolet light treatment

You can learn more about treating and filtering water in a recent post.

Where is the cleanest rainwater in the world?

According to Hydrotech, a recent study by scientists at the universities of Texas and Chile found that the cleanest water in the world is located in Puerto Williams, Chile. The cleanliness of the water is reflective of the air from where the rain falls.

According to the Director of the Arctic Bioculture Conservation Program, “water and air in this area are incredibly clean. It is an ecosystem that existed on the planet before the world industrial revolution.

Other countries that have been found to have clean drinking water include Denmark Iceland, Greenland, Finland, Columbia, Singapore, New Zealand, Sweden, and Canada.

All of these countries are renowned for their clean air and low levels of pollution and this all helps to contribute to clean water levels. As well as fewer pollutants in the air for the rain to absorb as it falls to earth, the low levels of pollution also help to ensure that any rainwater collected, including in reservoirs, lakes and aquifers, is much purer than in countries where pollution levels are much higher.

Is rainwater safe to drink?

In many countries, rainwater is perfectly safe to drink but it is not the case around the world. Here in New Zealand and in many developed countries including Australia, the USA and the UK, rainwater is safe to drink as long as the necessary precautions are taken to filter and treat the water collected from your roof.

There are different regulations in place in countries throughout the world when it comes to how rainwater should be treated.

According to the CDC, “The risk of getting sick from rainwater may be different depending on your location, how frequently it rains, the season, and how you collect and store the rainwater. Dust, smoke, and particles from the air can contaminate rainwater before it lands on your roof. Roofing materials, gutters, piping, and storage materials can introduce harmful substances such as asbestos, lead, and copper into the water. Dirt and germs can be washed into collected rainwater from the roof, especially when rain follows several days of dry weather.

It is always best to check with your local health authority which will usually provide additional guidance on safely collecting rainwater.

Rainwater collection is not allowed in all places. Some states consider rainwater the property of the state and regulate its collection, so you should consult with your local government (for example, your environmental quality department or health department) before proceeding. You can find out more about the states in which collecting rainwater is not allowed in a recent post.

Summary

Rainwater, in many instances, is the purest form of water, however, that is not to say that it is without impurity.

Many factors determine the cleanliness of the rainwater that falls from the sky, including the pollution in the air, as well as the surface on which the rain falls and how it is filtered once it has been collected.