by Evin Morrison, Extension Master Gardener
All photos by Evin Morrison, except as noted
The hardest part of keeping plants alive indoors is watering. A quick Google search and you will find article after article with the “best” way to water your plants, apps to remind you to water, and lots of tips, tricks, and hacks to keep your plants properly quenched. While that’s already a lot to digest and test in your own home, you then find out that there are different kinds of water to use. With all of this information, it’s hard not to get overwhelmed. Because there are pros and cons to each kind of water, let’s break it down, and then you can decide what works best for you and your plant collection.
Tap water
Most plants will be plenty happy with tap water. It is by far the easiest option; you can fill a watering can or simply place your plants in the sink or shower and give them a quick rinse. You can almost guarantee that the plants you purchase from the store have been watered with tap water, often getting sprayed with an irrigation system installed in greenhouses. So, continuing to water with tap water shouldn’t be a problem for your plants.
It is important to note that tap water is treated with various chemicals to make it safe for human consumption, most commonly chlorine or chloramine, and may also contain dissolved minerals like calcium and magnesium. These chemicals are the reason that so many people are concerned with watering straight from the tap, but fear not, watering in the sink is a safe and effective option. If your water smells of chlorine, you can simply fill your watering can and let it sit overnight. The chlorine will evaporate, and you can water your plants without any concerns.
It is possible for minerals to build up in your soil and affect your plant’s growth or lead to crispy edges on more sensitive plants like marantas or ferns. But if you are consistently repotting and refreshing soil, the small amount of buildup shouldn’t affect your plants, and neither should fertilizer buildup. For plants in a pot for an extended time without a refresh, tap water and too much fertilizer may alter soil pH and reduce beneficial microbial activity in the soil. That’s why checking soil and repotting once a year is an important practice.
If you are particularly concerned about chemicals in your water, you can get a water test kit. Water treatment plants and county waterworks should also supply their customers with water quality reports. The EPA requires water treatment plants to test regularly for per- and polyfluoroalkyl substances (PFAS), and these numbers are available online.
Distilled water
Many people, including houseplant collectors, swear by watering their plants with distilled water and purchase jugs of water or use refilling systems at the grocery store to take care of their plants. This obviously can get very expensive if you have lots of plants, requires a trip to the store, and if you use plastic jugs of water can lead to a lot of plastic waste—proof that there are pros and cons to every watering situation.
Distilled water is water that has been boiled into vapor and condensed back into liquid, leaving impurities and minerals behind. It’s essentially pure H₂O. This ensures that there are no harsh minerals or chemicals in the water you’re using, a must for a few specific plants. Carnivorous plants have delicate root systems that cannot handle tap water. Therefore, it is crucial to water them using distilled water or rainwater to keep them thriving. Distilled water mimics the natural rainwater that these plants encounter in their native environments, where the water is typically low in dissolved solids.
Many begonia, fern, and orchid collectors use only distilled water. If you choose to buy a specialty plant, it’s worth doing a little extra research or asking an expert or collector about watering needs and what kind of water to use.
Rainwater
Now, of course, all the plants in your home originally came from somewhere in nature and would exclusively get watered by rain or in some instances ground water. So, if you are up to collecting rainwater or moving your plants outside before a storm to get a good drink, they will thank you! Not only will a good rainstorm quench the thirst of your plants, it will knock dust and pests from the leaves. You can replicate this by showering your plants a few times a year with a hose, in the sink with a spray nozzle, or under a showerhead. Using rainwater is a great, sustainable option.
If you choose to collect rainwater, there are a few things to keep in mind. Do not use water collected from roof runoff, as it could have building debris that you don’t want to introduce into your plants. It’s also important to capture water in a closed system that keeps out pests like mosquitos or to treat your rainwater with a Bt (Bacillus thuringiensis) product like a mosquito dunk. You don’t want to accidentally bring in bugs just to water your plants. If you choose to collect rainwater in a bucket or other container, try to use it as soon as it fills. Water left out can grow algae and bacteria in the summer heat.
Like all options, there are a few drawbacks to relying on rainwater for houseplants. First, unless you live somewhere with consistent rain, you can’t rely on this method alone. Even with large rain collection barrels, in a drought month you might need to find an alternative. Second, moving plants in and out of the house might not be a great option for everyone, especially when large pots get heavy from saturated soil. So maybe give it a try for a few of your smaller plants and see how it goes!
This Monstera received a good drink from a passing thunderstorm, and the leaves were cleaned, too.
Tank water
Now this option is much more niche, but if you have a fish tank you might consider, as many plant lovers do, watering your plants with water from the tank. You can use this nutrient-rich water removed during regular maintenance of freshwater aquariums to give your plants a drink. It contains fish waste, decaying food, and beneficial bacteria which act as a natural fertilizer, providing nitrogen, phosphorus, and other nutrients that support plant growth. Not only that, but it will promote microbial activity in soil and can boost plant health.
This option should only be used if the tank is healthy. You don’t want to use the water if you have any sick fish or have used chemical treatments in the tank. Of course, this is only applicable with freshwater tanks as saltwater cannot be used on plants. Overly dirty tanks should also not be used to water plants as that could lead to smelly soil. So, while this is a great way to use water that normally would just get dumped, make sure you’re maintaining a healthy fish tank first.
A word of caution, however—excessive use of tank water may lead to nutrient buildup or imbalances in the soil. Yes, it is possible to overfertilize. If you’d like to give this method a try, give a little water from the tank to all of your plants, more like a shot of fertilizer, and then water them deeply using another method.
Utilizing fish tanks is also a great way to propagate plants. Many people set up systems that hold cuttings in the back of the tank where they take root. Lots of plants, like pothos and syngoniums, are happy having their roots in water and will grow that way for long periods of time. Not only do the plants love it, but the roots introduce oxygen back into the water for the fish. Just make sure your plant is clean of any chemical fertilizers before adding it to the tank, as those may affect the chemical balance of the water or the health of your fish.
Choosing the right water for your plants depends on the plant species, your local water quality, and environmental conditions. Understanding the benefits and limitations of each source will help you keep your plants thriving naturally and sustainably. Each choice has its pros and cons, but finding the best method for you and your lifestyle will ensure that you’re staying on top of your watering.