Written by: Alexandra Uta // Last Updated: Dec 30, 2022
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An ongoing debate in the gardening world is whether or not reverse osmosis water should be used for plants.
Some say it’s better due to fewer contaminants, and some say that it is worse due to the water not containing essential minerals that the plant needs.
So which is it? Let’s examine the pros and cons of using reverse osmosis water for your plants.
Key Takeaways
The short answer is yes, you can use RO water for your plants, but be sure to use it the right way and remineralize it. Using RO water without remineralizing it can lead to poor plant growth due to lack of nutrition.
Reverse osmosis water is great to use on plants when the water has high levels of contaminants, chemicals, and salts that could be detrimental to the plant’s growth.
Reverse osmosis filtration systems remove up to 99.9% of most pollutants, which means your plants can have very pure water. It also allows you to have a pure water base to add precisely the right combination of fertilizers and mineral salts that will help your plant to thrive and enable you to be totally in control of any variables in the water.
Reverse osmosis water is when a water source is pushed through a semipermeable RO membrane. This membrane has microscopic pores that stop contaminants from getting through to the other side and ending up in your clean water.
Most reverse osmosis systems also come with pre and post-filters that can get rid of other contaminants that the reverse osmosis membrane cannot. This leaves you with water that is free of virtually any contaminants that may be harmful to your or your plants’ health.
Reverse osmosis removes impurities such as chloramine, salts, and heavy metals. This is not only good for your plants but good for your health if you plan to eat the plants. Some water sources are high in lead and arsenic, which can transfer into your fruit and vegetables as they grow. An RO system will filter all these bad guys out.
Nearly all municipal water supplies have been treated with chlorine to kill any disease-causing bacteria. While this makes our drinking water safer, it isn’t good for plants in large quantities.
The level of chlorine in tap water won’t harm most plants. Still, it can cause the tips of the leaves of sensitive plants to die and turn black, such as prayer plants (Maranta), dracaenas (Dracaena), calatheas (Calathea), as well as carnivorous plants.
Using reverse osmosis water means you get complete control over the nutrient intake of the plant, with no disruptions from contaminants in the water. Using RO, we can also eliminate the chance of any potential reactions from pollutants with chemical fertilizers.
You may see improvement in the growth of your plants due to contaminants, such as salt, being filtered out of your water. Too much salt in the soil of your plant can stunt its growth.
There are some potential cons to using RO water for your plants, particularly if you do not remineralize or fertilize the plant appropriately.
RO filters out all the bad stuff, but it also filters out all the good stuff, leaving you with what some describe as ‘dead water’. As your plants need a variety of minerals to thrive, this means if you are using only RO water and not remineralizing it with fertilizer salts, you may be doing your plants more harm than good.
Reverse osmosis water usually has a lower pH than regular tap water, which makes it more acidic. Water that is too acidic makes it difficult for the plants to absorb nutrients, and it can also be corrosive to your pipes and irrigation.
Be sure to test the RO water regularly to ensure the pH is in the safe range.
A reverse osmosis system needs regular maintenance and filter replacements. This makes it more expensive than some other kinds of water. There isn’t any getting around the maintenance, especially the filter replacements, as if you don’t do it, the unit won’t effectively filter contaminants.
As mentioned earlier, RO removes pretty much all minerals from your water supply, both good and bad. Considering that plants need small amounts of multiple minerals in order to thrive, they need to be added back into your water!
This is usually done with calcium/magnesium solutions and fertilizer salts. Of course, different plants and crops will require different levels of dissolved solids to thrive, so be sure to check the salt index of your fertilizer and how much you need for your plants.
So does this mean that with proper remineralization, RO water is the best possible water for your plants? It is definitely up there, but let’s take a look at some of the most popular methods for watering plants and see where it ranks.
Well water can be okay, provided it doesn’t contain many contaminants. This means it will vary considerably from source to source. Testing it regularly is important to ensure your crops remain contaminant free.
Distilled water is considered better than tap water for plants, as just like RO, the contaminants are already filtered out. However, also just like RO, the good minerals will need to be re-added.
Rainwater doesn’t contain some of the fluoride or metals that tap water has, but it also does contain a lot of the minerals your plants need to grow. Still, clean rainwater is considered one of the best kinds of water for your plants.
Depending on how it is filtered, filtered water could be slightly better for plants than tap water. If you are looking at bottled, filtered water, that will end up being a costly exercise too.
Spring water is one of the best sources of water for plants. It is oxygen and mineral rich and has minimal impurities or harmful chemicals.
Tap water is acceptable for most plants, but not if it is high in contaminants or if you have chlorine or chloramide-sensitive plants. Basically, if you wouldn’t drink it, don’t give it to them.
It is not recommended to use softened water on your plants. If your water is naturally soft, it might be fine, but chemically softened water contains sodium that could be harmful to your plant growth.
If you have any thoughts about the question, can you use RO water for plants, please don’t hesitate to leave a comment below!
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