How To Make Tap Water Safe for Plants

All plants need water to survive — that’s a no-brainer. But did you know that the quality of the water can play a big role in plant health and longevity?

Most of us reach for the tap when it comes time to water our houseplants. Unfortunately, not all tap water is created equal. The presence of chemicals and pH levels can vary greatly from one area to another. Though we may not be able to tell the difference, our plants certainly can.

In this article, I’ll take the mystery out of how to make tap water safe for plants using a number of simple methods.

Why Is Tap Water Bad for Houseplants?

Before we go on, I want to make it clear that tap water is generally 100% safe. A plant responding poorly to tap water does not necessarily mean the water is unfit for other uses (including drinking).

With that said plant biology is naturally more sensitive to certain trace elements than the human body. There are also many chemicals and minerals that benefit us while doing harm to our beloved plants.

Here are the most common issues affecting plant health found in tap water:

Chemicals in Tap Water

Many treatment facilities add various chemicals to the water before sending it out to local homes and businesses. These additives are beneficial to us in one way or another. But not all houseplants can tolerate their elevated levels.

Fluoride, chlorine, or chloramine are the chemicals most commonly found in treated tap water. As a general rule, high levels of chlorine are bad for all plants. In my experience, some plant species are much more susceptible to excess fluoride than others. For example, Calethea is very sensitive to tap water and is sure to suffer over any prolonged period of watering. My Monstera, Pothos, and Dracaena struggle with my local tap water, whereas Peace Lillies, Ivy, Chinese Evergreen, and Ferns have no trouble at all.

Hard vs. Soft Water

To be clear, neither hard nor soft water is inherently better for plants. However, tap water that leans too hard in either direction can cause problems over time.

Hard water is water with a relatively high mineral content. Calcium and magnesium represent the bulk of this mineral content.

Hard water is infamous for leaving behind limescale and other forms of buildup on faucets, kettles, and other surfaces. These mineral salts can also accumulate in potting soil, taking a toll on the root systems of more delicate plants.

Soft water is water that has had these minerals removed. Most soft water is created by exchanging calcium and magnesium for other chemicals like sodium and potassium.

While soft water is generally seen as safe for use on plants, its the addition of sodium that can cause problems if it builds up in the soil.

pH Levels

The pH of your tap water can also affect plant health in extreme cases. Plant species that prefer highly acidic or alkaline growing conditions will naturally be more sensitive to water pH levels. 

Per recommendations from the EPA, tap water should have a pH between 6.5 and 8.5. However, some areas are prone to readings outside of this range. If you suspect that your tap water is impacting your houseplants, I recommend testing the pH to be sure.

Making Tap Water Safer for Plants

If your tap water quality is so-so, one option you have is to switch to bottled water for all of your irrigation needs. As someone who has lived with extremely hard water in the past, I can confidently say that this solution is cumbersome and expensive!

In my opinion, the better option is to invest in making your tap water safer for your houseplants. There are several ways to do this, depending on your budget, starting water quality, and how many plants you have in need of watering.

1. Let It Sit Out

It sounds deceptively simple but one of the easiest ways to remove excess chlorine from tap water is to let it sit out for at least 24 hours. This works because chlorine readily evaporates under normal household conditions.

You can fill up a large bowl or your favorite watering can the day before you plan to water. If you have a lot of houseplants, you may need to stagger your watering schedule (or invest in more watering cans!).

Note that this method is not effective at removing fluoride or chloramine from tap water. Unlike chlorine, neither of these chemicals readily evaporates into the air.

2. Install High-Quality Filtration

Water filtration is a huge industry right now. You can improve your tap water’s quality by using anything from a filtered pitcher to a whole-home filtration system. 

While there are several ways to measure the efficacy of a water filtration system, the two best options for plant health are activated carbon filters (ACF) and reverse osmosis.

Activated Carbon

Activated carbon is an extremely porous material that resembles ground-up charcoal. It is one of the most affordable and widely available filtration materials currently available.

Activated carbon filtration can remove chlorine and some other metal compounds from tap water. These filters are not effective against fluoride and will not improve hard water by removing calcium and/or magnesium.

Reverse Osmosis

Reverse osmosis systems force water through a semipermeable membrane that removes contaminants like sodium and lead. This filtration type may reduce the content of chemicals and minerals like fluoride, calcium, and magnesium.

By itself, a reverse osmosis filter won’t be very effective against chlorine. However, most modern systems utilize pre- or post-filters that easily take care of unwanted chlorine in tap water.

Reverse osmosis is regarded by many as the best at-home filtration option for plant health. The main drawback is the price. Standalone units can easily cost up to $500 while whole-home filtration systems often cost several thousand.

3. Use pH Adjusters

If your tap water’s pH level is the main concern, adjusting the pH by hand is likely the best solution. While there are several pH adjusters you can use, I recommend testing out these household products first:

  • To increase acidity: Add white vinegar to tap water to lower the pH
  • To increase alkalinity: Add baking soda to tap water to raise the pH

You’ll need to experiment with various ratios to achieve the desired pH level. Start with a small amount — i.e., a tablespoon — of either vinegar or baking soda per gallon of tap water. Use trusted pH testing strips to monitor your progress as you adjust.

Symptoms of Poor Water Quality

Visible symptoms of poor tap water quality often resemble those of fertilizer burn. This is because both conditions are commonly caused by mineral and chemical buildup in the soil.

Potential signs of poor water quality in houseplants include:

  • Yellow or brown leaves
  • Dry leaf tips or margins
  • Stunted growth
  • Wilting or drooping foliage
  • White residue on the soil surface

Keep in mind that these symptoms can also be attributed to things like nutritional deficiencies, improper watering schedules, over-fertilization, and other environmental stressors so you may need to undertake some further investigation before acting.

FAQs Tap Water for Plants

Is Boiled Tap Water Better For Plants?

Contrary to popular belief, boiling tap water in a pot or kettle will not remove harsh minerals and chemicals like chlorine, fluoride, sodium, magnesium, and calcium. While boiled water won’t harm your plants (as long as it’s cooled down), it also won’t do noticeable good.

Citations

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.