Best Water for Plants: Filtered vs. Distilled vs. RO

Posted by
John Woodard on December 01, 2023

When filling up a watering canister for your plants, you may be tempted to think that water that is safe for humans is also safe to use for your garden. However, plants are more sensitive to the water they intake than mammals, so special care must be taken when hydrating your plants. Some chemicals found in city and well water can harm your plants in the long run. In this article, you can discover which contaminants are most harmful to plants, how to remove these contaminants from water, and the best filters for treating the water you use for your plants.

Key takeaways

  • You should avoid watering your plants with water that contains high levels of chlorine, chloramines, fluoride, heavy metals, or water-hardening minerals. Tap water often contains all these contaminants.
  • You can know which contaminants are in your water with either an at-home or laboratory water test kit.
  • Reverse osmosis systems and water distillers are the most effective water treatment options that provide consistently high-quality water for your plants. Activated carbon filters are also an acceptable option in some cases.
  • Regardless of the water treatment method you choose, always supplement your plants with the appropriate nutrients.

Should I use filtered water on my plants?

If your water source contains chlorine, chloramines, or fluoride, you should use a filter to remove these contaminants before watering your plants. If you collect rainwater to use for your plants, you do not need to filter the water unless the rainwater is subjected to harmful contaminants on your roof, in your gutters, or in the air. Not all water filters remove harmful contaminants to plants, so ensure you use an appropriate system to elongate the life of your plants.

Is tap water bad for plants?

To keep your plants healthy, you should not use city-treated tap water on plants without filtering the water first. Water treatment plants add chlorine and chloramines to water to kill bacteria, viruses, parasites, and other microorganisms. Fluoride is also added to prevent tooth decay. While these chemicals are effective at what they do, they are not good for soil. Chlorine and chloramines eliminate beneficial bacteria in soil, damaging the roots over time. Likewise, fluoride stunts growth and can cause visible damage to your plant life.

Learn more: How to remove chlorine from water | How to remove chloramines from water

Is well water bad for plants?

If you get your water from a well, it may contain contaminants that harm your plants. If your well water contains high concentrations of chlorine, fluoride, nitrates, nitrites, iron, or salt, you must use a filter to protect your plant life. The pH level of your water should also be taken into consideration. Too high or too low of a pH can leave plants miscolored, brittle, and lifeless. If you are unsure what is in your well water, get your water professionally tested.

How do I know what is in my water?

You can test your home’s water with either an at-home water test kit or a laboratory water test. At-home test kits allow you to target specific contaminants with your testing, while laboratory tests give a more thorough rundown of the makeup of your water. Well water should be professionally tested at least once per year for coliform bacteria, nitrates, total dissolved solids, pH levels, and any other region-specific contaminant. If you simply want to know the general makeup of your city-treated water at home, a home water test kit may suffice.

Learn more: Lab water tests vs at-home water test kits

What are the symptoms of an unhealthy plant?

If you use water that contains the wrong types of contaminants for your garden, your plants may show the following symptoms:

  • Stunted growth
  • Yellowing or wilting leaves
  • Infections
  • Browning that starts at the tips (crisping)

If your plants show any of these symptoms, consider testing your water and installing the appropriate filtration system in your home.

yellowing plant

What is the best water for plants?

The best water for plants is as free from contamination as possible. This purity can be achieved by a number of water treatment systems. With a clean base, you can supplement the clean water with the appropriate nutrients for the specific plant that you are growing. Certain contaminants, such as iron, can block roots from absorbing nutrients if the contaminant is present in high enough levels. If you supplement your plants with enough nutrition while also giving them clean water, you can more precisely control the nutrients they consume.

Best water treatment for plants

The best water filter for your plants is determined by the contaminants in your water source. For example, if your water contains chlorine, chloramines, and fluoride, you must use a filter that can reduce the levels of these contaminants. If your water contains high levels of iron, a common well water contaminant, you will want to reduce those levels before the iron reaches your soil. Reverse osmosis and distillation remove practically all impurities from water, so they are a safe bet regardless of your water source. Activated carbon filters remove many contaminants that are toxic to plants, making them a less expensive option with a few drawbacks.

Reverse osmosis systems

Reverse osmosis (RO) systems reduce the levels of almost all contaminants in water. Regardless of the incoming water quality, an RO system can provide water that is safe for plant life. Because reverse osmosis water is so high quality, it provides consistent water that allows precise control over the nutrients you feed your plant. If the water supply feeding an RO system contains high levels of water-hardening minerals, you will want to incorporate a water softener before your RO system. Without a water softener, these minerals can clog the pores of a reverse osmosis membrane, reducing the effectiveness and efficiency of the system drastically. If your water supply is not hard, an RO system is an excellent standalone solution for your plants.

Learn more: What is reverse osmosis?

Note that, while RO systems reduce a vast majority of contaminants from water, they do not remove some microorganisms. If your water is pumped in from a well, you will need to have some type of disinfection system in place to make water safe for drinking. While these microorganisms will not harm your plants, they will affect the health of those in your home who consume the water.

Advantages of RO for gardening
  • Yields consistent, high-quality water
  • Allows precise control over plant nutrition
Disadvantages of RO for gardening
  • More expensive than activated carbon
  • Slower filtration speed than activated carbon

Water distillers

Water distillers yield extremely pure water, so they are an excellent source of water for plants regardless of water source. Because it contains so little contamination, distilled water will not supply any nutrients to the soil. As a result, you must make sure that you supply the soil with all the nutrients that it may otherwise get from less pure water.

Learn more: What is a water distiller and how does it work?

Some plant enthusiasts do not believe in using distilled water because it washes nutrients away from the soil. However, distilled water does not contain trace amounts of heavy metals, unwanted chemicals, and other contaminants that can harm a plant over time. If you use appropriate supplements alongside distilled water, your plants will grow healthy and strong without side effects from lingering water contaminants.

Advantages of water distillers for gardening
  • Provides the purest water possible
  • Allows precise control over plant nutrition
Disadvantages of water distillers for gardening
  • More expensive than activated carbon
  • Slower production speed than RO and activated carbon
  • Use energy during production (about 3 kWh per gallon)

Activated carbon filters

Activated carbon filters use a porous carbon media that attracts contaminants through a process called adsorption. While they do not remove nearly as many contaminants as reverse osmosis or distillation, they can be a beneficial filter for your plants. Carbon filters are most commonly used to remove the chlorine and chloramines added to municipal water. The removal of these chemicals enhances water’s taste for human consumption, but it also prevents them from killing beneficial bacteria in soil. Carbon filters rated at one micron or lower can also remove common well water contaminants, such as iron, lead, and arsenic.

Learn more: Activated Carbon Filters 101

The downside of activated carbon filters compared to reverse osmosis and water distillers is the inconsistent final product. This is not because the carbon filters are inconsistent themselves, but because some contaminant levels in the water supply may fluctuate over time. For example, the water hardness levels of a water supply one month may rise due to changes where the water is sourced from. If you are only using an activated carbon filter, your plants will be subjected to varying levels of hardness over time. If you were to use a reverse osmosis system or a water distiller, these levels would remain consistent regardless of the fluctuations in the water supply.

Advantages of carbon filters for gardening
  • Inexpensive
  • Filter at high flow rate
Disadvantages of carbon filters for gardening
  • Not as thorough as RO or water distillers
  • Inconsistent results depending on water supply


If you have any additional questions, please do not hesitate to contact us.

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