Water Security: How to Purify Rainwater for Plants

Water Security: How to Purify Rainwater for Plants

Table of Contents
Table of Contents

Using your rainwater storage is an underappreciated source for watering your plants. However, for the best gardening results, you will need to purify your rainwater to remove chemicals, sediments, and other contaminants. Once filtered and purified, it can be used for potable and non-potable uses such as watering plants, flushing toilets, farming, and cleaning. 

Rainwater will last a week after being collected. Afterward, it will emit a foul odor and become a breeding ground for mosquitos and algae. 

To make it last longer, it will need some filtration process to purify it. While filtering rainwater for drinking water use requires complex systems, filtering rainwater for non-potable use requires only a minimal filtration process. For homesteaders, collecting, storing, and using rainwater can help sustain their survival plants for the long run while conserving water consumption.

boy watering plants

Why does Rainwater need to be Purified?

While rainwater falling from the clouds is pure and free from chemicals that, make it suitable for your plants. However, it can be exposed to air pollutants or interact with other murky substances before touching the ground. These air pollutants may come from chemical facilities, factories, or power plants if you live nearby these infrastructures. 

Also, as rainwater hits your catchment area, it could be exposed to branches, dust, insects, soil, and bird waste. 

When you collect and harvest rainwater through a system of pipes and store them in your water storage location, pre-filtering the rainwater entering the conveyance system is a must if you want to eliminate large pieces of debris.  

How to Collect Rainwater for Plants?

To harvest rainwater at home, you will need to set up a catchment area and conveyance system where rainwater can be collected and transported through a system of drains and pipes. For most people, the best catchment area is their roof. Next, you will need a conveyance system like gutters or drainage lines of the roofs that are responsible for collecting rainwater that flows to the linked downspout pipes. These downspout pipes or conduits will carry the collected rainwater to your storage tanks or barrels, which will serve as your reserved water source for your future household demands. The size of the barrels may depend on your watering needs, and it is recommended to avoid metal or concrete water tanks as they can rust quickly. 

Rain barrel in tropics

Step-by-Step Guide on How to Purify Rainwater for Plants

Below is a four-step guide for purifying harvested rainwater.  


The most important part of the process is to pre-filter rainwater before it reaches the storage tanks. With this, you can remove leaves, twigs, and dust from entering the storage tank. 

Filters can be installed over the gutter, so rainwater is filtered before it reaches the downspout that pours water into the storage tanks. We recommend using stainless steel mesh screens as these are more durable and require less upkeep.

A solid filter will make sure that large debris or detritus like leaves, dust, animal feces, and sand cannot reach the captured rainwater. In order to eliminate even smaller particles that mesh screens are unable to catch, further filters with decreasing particle sizes can be installed. 

It is crucial to consider where the rainwater filter installation will be installed for easy monitoring and cleaning maintenance. The filters eventually need to be cleaned every 3-6 months, depending on how close your roof is to trees and other barriers. 

water filters


The second step is treating the harvested rainwater after it’s been placed in your storage tanks. Stored rainwater in the tanks or barrels can still have tiny particles left that were not cleared away during the first filter. These residual particles, which are heavier than water, will commonly settle at the bottom of the water tank. While it poses a problem on how the water will continue to flow to its next stop, the stored rainwater could also develop foul odors. To prevent this from happening, you need to oxygenate the rainwater by installing a Calm Inlet at the bottom of the water tank. You must ensure that the water entering your tank passes through a Calmed Inlet at the tank’s base.

Installing a Calmed Inlet device is recommended if you have large water tanks, as it ensures that the water entering the tanks jets upward from the bottom of the tank and oxygenates the water above the sediment without actually upsetting the settled particles. When it rains, the water naturally moves above the Calmed Inlet, which is sufficient to maintain water oxygenation. 


While the heavier-than-water residual particles settle at the bottom of your storage container, the lighter-than-water particles that are not caught by your mesh filter will tend to float at the surface of your water tanks. In order to remove the floating particles, you will need to scrape floating particles from the water in the container.

Watering Garden


The fourth and last step is crucial if you are pumping rainwater for your garden or plants. A moving fine mesh will ensure that only the pure water is fed into your water pump. 

Unlike static mesh filters that are integrated into some pumps, floating intakes allow the filter mesh to move within the purest portion of the stored water. Any particles smaller than your filter will either sink to the bottom of your water tank or float to the top of the water you have stored. That is why the middle part of the tank will have the ideal purest water.

Fine mesh filters with hose attachments called ‘floating intakes’ can be customized in length to meet your storage tank. It’s crucial to watch how the tiny mesh filter moves. Any little debris that hasn’t found its final position is at risk of falling into the water or getting caught in the mesh since the pump draws water into it.

If the fine mesh remained stationary, the debris would eventually clog it. However, because a floating intake is permitted to move in water, any material that may have been drawn up against the mesh will be forced off it as the float sways back and forth.

Watering Survival Crops

People also ask 

Common questions we come across are:

Rainwater for plants can only be kept in storage for about a week before it starts to become contaminated. These can be contaminated by factors like algae, mosquitoes, or animals. Algae will spawn when exposed to light, and mosquitos are likely to enter the barrel and make it their breeding ground. Meanwhile, animals like insects will attempt to enter any storage container when they need to drink and can subsequently contaminate the water if they fall in. Even though it might not seem like it, you shouldn’t use contaminated water to water your plants, especially so if you are watering edible crops. The plants that you use the water on could die if you do.

Preventing stagnation is a critical stage in storing rainwater. In addition to producing an unpleasant smell, stagnant water serves as a breeding ground for algae, insects, and diseases. In order to prevent stagnation, it is recommended to use food-grade rain barrels because they are made to collect water while effectively blocking sunlight. Do not forget to put a lid and screen on the container to keep out leaves, twigs, and other debris that could contaminate the water. It is also important to monitor and maintain the cleanliness of the catchment area to prevent water contamination from debris entering the tanks. To get rid of mosquitoes and larvae, you can use safe and non-toxic insecticides. Lastly, utilize rainwater frequently and clean your water tanks or barrels regularly.

Consider cleaning your water storage container once a week if they don’t have adequate lids. Regular cleaning will halt algae growth and mosquito breeding. You can simply clean by filling the buckets with dish soap, scrubbing them, and rinsing them several times to make sure you get rid of any soap residue. If you’re doing it on your own and using an electric pump, be sure to turn the power off first. Make good use of the water that is still in your tank by using it around your garden or for cleaning purposes. After that, flush away any leftover contaminated water. The best water pressure is one that can readily remove any debris from the tank’s side. You must use a tube inserted into the tank inlet to pump out the materials that are sitting on the bottom in order to remove sludge without losing the rainwater you have already collected. Utilizing diverters is another method to reduce the accumulation of sludge. Leaf strainers and UV filters are also efficient ways to keep tanks clean. Lastly, you can also opt to avail professional cleaning services for your tanks.

Rainwater is best when filtered. Although filtered rainwater is not necessary, the pollutants that rainwater captures as it falls from the clouds can be harmful to plants. Additionally, rainwater has a short shelf life and will collect bacteria and insects if it is not properly purified. Between the added pollutants and organisms, using unfiltered water can be harmful to survival crops, causing them to become sickly. So, it is recommended to use a good filtration system to remove pollutants and organisms before utilizing rainwater to grow plants.

Rainwater is purer than tap water. This is because chemicals are used to treat tap water, while rainwater is purified as it is distilled from the sun. When it rains, carbon dioxide is transported to the atmosphere for the benefit of plants. Carbon dioxide can aid in the release of crucial nutrients for plants once it reaches the soil. Nitrogen, which is necessary for plant growth, is also present in rainwater and it has a higher oxygen content than tap water, which fosters complete green growth in plants.

Rainwater can be kept for up to a week before it becomes contaminated and is no longer usable for watering plants. Pure water, like rainwater does not expire. However, water containers don’t last forever, coupled with potential exposure to animals like insects, light, and other types of debris that can ruin its purity. You can store it longer time if precautions are taken. It is best to paint your barrels with dark colors to avoid direct exposure to the sunlight that triggers the growth of algae. Mosquitoes also like to breed in still waters, so make sure they don’t dwell in them as mosquitoes can cause serious and fatal diseases. You can also treat rainwater with an appropriate amount of chlorine. Lastly, do not forget to wash your barrels once to twice a year or as often as you wish, and check your rainwater collection regularly. 

natural survival garden produce

Wrapping Up

Although it is not required, it is important to purify rainwater before watering plants for the best results. Whether you are a casual gardener or looking to start a survival garden, purifying rainwater before use will help your plants thrive. Additionally, untreated rainwater will keep for about a week, but through the proper purification and storage methods, its shelf life can be extended. Since few water sources are as pure as rainwater, it would be a huge benefit for your garden and something you should consider.

Still, it is important to note that although the water has been purified, it may not be safe for drinking. Converting rainwater into drinking water requires a more refined filtration process to remove pathogens and ensure it is safe for consumption. 

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