Your plants need water to grow and survive like everything else on this planet. However, the quality and components of the water you use significantly impact the health of your plants. Tap water is often disinfected with chlorine, which makes it safe for human use, but not necessarily for plants.
You should always boil tap water before watering plants because tap water likely contains chlorine and fluoride, and salts like calcium and magnesium, which can cause toxicity in plants. Chlorinated water also kills essential soil microbes, decreasing soil quality.
While you can use tap water to water your plants occasionally, it is always recommended that you treat it in some way to keep your plants healthy. This article explores the effects of tap water on plants, the pros and cons of boiling water, and other ways to improve tap water for plants, so read on!
Pros and Cons of Boiling Tap Water for Plants
Boiling water is one way of treating tap water to make it safe enough to water your plants. However, there are pros and cons to doing so. Before we dive into those, let’s first look at the effect tap water can have on plants.
Effects of Using Tap Water for Watering Plants
There are several reasons why unfiltered and untreated tap water is not recommended for watering plants. Here are the effects of tap water on plants that demonstrate why you shouldn’t use it for watering:
- Chlorine toxicity: Chlorine is added to water to kill disease-causing microbes. However, it does not discriminate regarding bacteria, so watering plants with chlorinated water will also kill all the necessary microbes in the soil. Over time, chlorine buildup leaches nutrients and affects overall plant growth.
- Fluoride toxicity: Fluoride is commonly added to tap water, but many plants are sensitive to fluoride. Symptoms of toxicity include ‘burnt’ leaf tips and edges. These symptoms are more noticeable in times of drought and heat stress.
- Salt buildup: All water, even rainwater, contains salts and minerals, but these salts appear in a higher concentration in tap water, especially hard tap water. An increase in salinity can lead to dehydration and burning in your plants as they struggle to retain water and move nutrients as necessary.
- Increase in soil pH: As most tap water contains salts such as calcium, it tends to be more alkaline. Watering plants with tap water can increase the pH value of the soil over time, which is not ideal as most plants prefer neutral-value soils. Many tropical plants even prefer slightly acidic soils, which makes tap water a bad idea for watering.
Grass can hold up better against chlorine toxicity than other plants or trees, but the primary concern is the buildup of chlorine in the soil over time. You can learn more about this in my article about whether it is possible to overwater new turf: Is It Possible to Water New Turf Too Much?
Watering your plants with tap water can also affect any nutritional supplements you may add. For instance, if you’re watering in any mycorrhizae like the Great White mycorrhizae, the fungi will be killed or burnt by the chlorine, fluoride, or salts in tap water.
All the adverse effects of tap water are why watering plants with tap water is not ideal. Plants vastly prefer rainwater, but when it is unavailable, you must treat the tap water in some way to make it safe for plants. One of the easiest ways is to boil the water.
Now, I’ll detail the pros and cons so you can decide if this is the method for you.
Pros of Boiling Water for Plants
There are several advantages of boiling water for plants:
- Removes chlorine: Boiling water helps remove a lot of the chlorine in tap water. Beyond a certain temperature, chlorine becomes less soluble and evaporates into the air, so heating your water is one of the simplest ways of removing chlorine. Of course, all the chlorine won’t dissipate, but the concentration will come down to a safe level.
- Reduces water hardness: Sedimentation of salts occurs on the heated surface of the pot you’re using to boil your tap water. It is a quick way of reducing the salinity of your tap water without having to invest in filtration devices.
- Kills harmful bacteria: You can make most water safe for drinking by boiling it. Boiling water kills pathogens, viruses, and most disease-causing bacteria, which might affect the health of your plants. Boiling is a good way to make tap water about as pure as rainwater.
Cons of Boiling Water for Plants
While there are definite benefits to boiling tap water for watering plants, this method has its limitations, as noted earlier. Here are some cons of boiling water for plants:
- Doesn’t filter heavy metals: While boiling water is good for removing most impurities, it cannot filter out any metals. If you suspect your water is contaminated, use a filtration system such as carbon filtering to keep yourself and your plants safe from heavy metal poisoning.
- It may increase fluoride concentration: Unlike chlorine, which evaporates easily, fluoride is unaffected by boiling water. In fact, boiling your tap water can increase the concentration of fluoride as some water evaporates, reducing the amount of water that dilutes the fluoride.
- Only feasible for small amounts of water: You can only boil as much water as the size of your pots and the amount of time you have. Boiled tap water also needs to be cooled before use, so you’ll also have to factor in that time. Boiling tap water is only feasible if you have a few houseplants, not if you want to water an entire garden.
Other Ways to Improve Tap Water Before Watering Plants
As we’ve noted, boiling tap water is often insufficient to make water safe enough to water your plants, especially if you suspect high levels of fluoride or metals in your water. Even if your water is safe, boiling it is pretty cumbersome.
Instead of boiling your tap water, you can use other methods to treat it so that it’s safe enough to water your plants. However, no single approach will eliminate all contaminants. Therefore, consider boiling your water with other methods listed here.
Let the Water Sit
If you’re sure that your water isn’t as contaminated as normal tap water, you can allow it to sit in the sun for up to 24 hours. The chlorine evaporates, but this will not filter out any metals or fluoride, so only use it for a less labor-intensive – not safer – alternative to boiling water.
Use an Activated Carbon Filter
This is one of the best ways to filter tap water and make it safe for everything from drinking to watering your plants, especially for chemical impurities. Activated charcoal absorbs chlorine, fluoride, and heavy metals from the water.
However, you may still need to let your water sit to eliminate any particulate matter or salts because the carbon filter will let those pass through.
Apply a Membrane Filtration System
Membrane filtration systems use a form of reverse osmosis to strain particulate matter, metals, salts, and fluoride from your tap water and make it safe to drink and water plants. These are one of the most effective ways of treating tap water, but the membranes are sensitive to chlorine and can wear down over time.
Use Bottled or Distilled Water
If you only have a few plants, consider buying bottled water to water your plants. This is expensive and not ideal, but definitely better than using tap water on chlorine or fluoride-stressed plants.
Distilled water is water that is purified of all impurities through the process of evaporation and condensation. It is safe for your plants, but plants need some trace amounts of minerals to grow, so you’ll have to supplement them to keep them healthy.
You should boil tap water before watering plants to protect them from chlorine toxicity and kill potential pathogens. However, boiling tap water will not eliminate heavy metals or fluoride, so you should consider using additional treatments to make your water safe. You can use activated carbon filters or membrane filtration systems in addition to boiling your tap water.