We’ve all heard the arguments regarding tap water. Some people use tap water all the time with their plants and claim it’s perfectly fine.
Others grab their crucifix and start conducting exorcisms on anyone who comes near a plant with tap water.
But every story has three sides, and that third side – the truth – is almost invariably somewhere in the middle.
Let’s take a moment to get down and dirty with the muddiest type of water in plant care controversies.
Is Tap Water Bad for Plants?
The short answer is yes, but there’s a much longer answer which can be more ambiguous.
That second answer regards why and how you can make tap water safe for use.
Five Types of Water
Before we begin, it’s important to look at five different types of water for plants and their qualities.
The five are listed below from best to worst.
Rain Water – Containing dissolved nitrogen, higher acidity, and lacking any chemicals or mineral salts is the perfect choice for plants. Rainwater is excellent clean water for watering Calathea plants.
Augmented Distilled Water – By adding hydrogen peroxide to distilled water, you end up with something very close to rainwater, although this mix should only be used every few waterings.
Distilled/Baby Water – Distilled water (sometimes called baby water) has been boiled to steam, then recondensed.
The result is a microbe, mineral, and chemical-free form of bottled water that is safe for plants but also lacks the benefits of the first two types.
Well Water – Well water is usually free of chemicals, but it often has higher microbial content and can have a lot of mineral salts.
Tap Water – Bottom of the proverbial barrel, tap water lacks acidity and is full of mineral salts and chemicals such as fluoride and chlorine gas which are toxic to plants (and people too, for that matter).
As you can see, tap water has all of the bad and none of the good, but that’s only the beginning of the evidence.
Dealing with Chlorine
Let’s say you’re stuck between paychecks and aren’t very good at potting (AKA distilling) your water.
This is when the big chlorine panic starts, but it is the least of your tap water problems.
Plants actually need a little bit of chloride, but too much can cause a condition called chlorine toxicity, in which the plant’s leaves may become brown or even scorch.
Even worse, some tap water contains chloramine, a potent mixture of chlorine and ammonia.
However, unless you’re flooding your plants, the main damage from chlorine will be to the soil itself.
Chlorine kills microorganisms (the very reason your tap water was treated with it in the first place), including the ones you’ve just added with worm castings, compost, or bacterial teas (such as manure tea).
For more info on the effects of chlorine on plants, check out this document by the EPA.
The good news is that chlorine is one thing you can easily remove from the water.
Chlorine in water will evaporate if left sitting, so fill a pitcher or large bowl with tap water and let it sit out overnight or up to 24 hours, and the water will be chlorine-free.
Now we come to the most dangerous chemical in most tap waters: fluoride
Municipalities add fluoride to water in the hopes it will help prevent tooth decay.
No, that’s the only reason.
Fluoride can be pretty toxic to humans, animals, and indoor plants alike when ingested in anything above minute quantities.
For plants, it can cause necrosis (dead tissue) in leaves and result in chemical burns, as mentioned in this Michigan State University article.
The worst part is that potting your water won’t eliminate any fluoride content.
This is where water filters come in.
Brands such as Brita offer faucet or pitcher filters that use reverse osmosis, a process that can safely remove both fluoride and iron from water.
If you know your local tap water contains fluoride, it’s best to invest in a quality filter that can remove it, both for your plants and your family’s health.
The term mineral salts do not refer to sodium chloride.
Instead, this is a term generally given to mineral waste particles that can build up in the soil over time to create a toxic environment for your plant.
Most tap water contains calcium, magnesium, and sodium.
However, traces of iron, potassium, selenium, silica or other minerals may also be present.
Some of these minerals, such as potassium, can benefit the plant, but most can be harmful as they build up.
The harder your water is, the more minerals it has.
However, this is another time when filters come in handy. A Brita or Zero Water filter can reduce the particle content to safe levels for both you and your plants.
For plants that use the soak-and-dry method of watering, part of the point is to flush these minerals out of the soil, so you don’t want to be using water that will just put them right back in.
Finally, we come to acidity.
Rainwater is so wonderful because it’s ever so slightly acidic, making it easier for plants to process, especially azaleas and rhododendrons, which thrive on slightly acidic water.
This is also one of the many benefits of adding some lemon or lime juice to a glass of water, as it’s easier for humans to absorb as well.
You can make the water a little more acidic by adding 1 cup of vinegar or 2 tablespoons of lemon juice to a gallon of water.
Be sure to pour onto the soil and avoid splashing the leaves, as the acid can cause burns.
As a fun side note, lemon juice is high in potassium and can benefit humans in many of the same ways it helps plants, so share a toast with your plant and have some lemon water as well.
So… Is Tap Water Bad?
Now that we’ve looked at all the dangers of tap water and found each one has a solution, the answer is both yes and no.
When possible, avoid giving your plants straight tap water (and you should be avoiding it too!), but while it can harm them over time, it won’t kill most plants on its own.
Instead, if you want to use tap water, invest in a good water filter and follow the above treatment methods to make the water something both you and your plants can enjoy.