Water Quality: Tap vs Distilled

Water Quality: Tap vs Distilled

I killed my first calathea with tap water. I didn’t know. I watered it religiously, kept it away from the window, misted it like the internet told me to. And then, slowly, the edges turned brown and crispy. I thought I was underwatering. So I watered more. The brown got worse.

Turns out, my city tap water was the problem. Not the amount. The quality.

If you’ve noticed brown tips on your plants even though the soil feels right, or if you’re trying to figure out whether you need to spend money on distilled water, this is for you. I’m going to walk through what I’ve learned about water quality after years of trial and error (and a few dead plants).

Fluoride damage (Brown tips)

Here’s something most people don’t know: many cities add fluoride to drinking water. It’s great for your teeth. It’s terrible for certain houseplants.

Fluoride builds up in the soil over time, especially in plants that are sensitive to it. The tips of the leaves turn brown and crispy, starting at the very edge and working inward. It looks exactly like underwatering or low humidity, which is why so many people (including me) misdiagnose it.

The plants that hate fluoride the most are dracaenas, spider plants, calatheas, and prayer plants. If you have any of these and you’ve been using straight tap water, there’s a good chance fluoride is your problem.

The tricky part is that fluoride damage is cumulative. You won’t see it right away. It builds up in the soil over weeks or months, and by the time the tips start browning, the damage is already done. You can’t reverse it. You can only trim off the brown parts and switch to better water going forward.

I learned this from a horticulture extension article from the University of Massachusetts, which explained that fluoride toxicity shows up as tip burn because the fluoride concentrates at the leaf margins where water evaporates. The plant pulls water up through its system, and the fluoride gets left behind at the edges.

So what do you do? You have a few options. The easiest is to use distilled water, rainwater, or filtered water that removes fluoride (most basic carbon filters don’t). If you’re using tap water, you can let it sit out overnight, but that only helps with chlorine, not fluoride. Fluoride doesn’t evaporate.

Another trick is to water your plants thoroughly and let excess water drain out. This helps flush out some of the built-up salts and fluoride, though it’s not a perfect solution. You’re still adding more fluoride every time you water.

I switched to distilled water for my calatheas and dracaenas, and I use tap water for everything else. It’s a compromise. Buying gallons of distilled water every week gets expensive, so I save it for the plants that actually need it.

Collecting rainwater

Rainwater is free, and it’s basically the best water you can give your plants. It’s soft, it has no chlorine or fluoride, and it’s slightly acidic, which most houseplants prefer.

I started collecting rainwater last year after I got tired of buying distilled water. I put a bucket outside on my balcony when it rains, and I usually get a gallon or two depending on the storm. It’s not enough for all my plants, but it helps.

The main thing you need to know is that rainwater can pick up dirt, bird droppings, and debris from your roof or balcony. I strain mine through an old T-shirt before I use it, just to get out the chunks. Some people worry about pollution or acid rain, but unless you live next to a factory, rainwater is still cleaner than most tap water for plant purposes.

One thing I didn’t expect: rainwater goes bad if you let it sit too long. I left a bucket of it in my closet for a month, and it started to smell swampy. Algae or bacteria had grown in it. Now I use it within a week or two, or I store it in a sealed container in a dark place.

If you don’t have outdoor space, this obviously won’t work for you. I lived in an apartment with no balcony for years, and I just had to use distilled or filtered water. But if you can collect rainwater, it’s worth the effort.

Above: A close up look at the symptoms.

Letting chlorine evaporate

Most city tap water has chlorine in it. Chlorine keeps the water safe to drink, but some plants are sensitive to it. The good news is that chlorine evaporates on its own if you let the water sit out.

I fill up a pitcher or a gallon jug with tap water and leave it on my counter overnight. By the next day, most of the chlorine has evaporated. This works because chlorine is a gas at room temperature, and it escapes into the air pretty quickly.

The problem is that some cities use chloramine instead of chlorine. Chloramine doesn’t evaporate. It’s a combination of chlorine and ammonia, and it stays in the water no matter how long you let it sit. You need a specific filter to remove chloramine, or you need to use distilled or rainwater.

I didn’t know about chloramine for the longest time. I kept letting my water sit out, thinking I was doing the right thing, and my plants still looked stressed. Then I called my city’s water department and asked what they use. Turns out, they switched to chloramine a few years ago.

If you’re not sure what your city uses, you can usually find out on the water department’s website, or you can call them. It’s public information.

For plants that aren’t super sensitive, chlorinated tap water is usually fine. Most common houseplants (pothos, philodendrons, monsteras) don’t care much about chlorine. But if you’re growing ferns, calatheas, or carnivorous plants, you’ll want to use dechlorinated or distilled water.

Is hard water bad?

Hard water has a lot of dissolved minerals in it, mostly calcium and magnesium. You can usually tell if you have hard water because your shower gets a white, crusty buildup, or your dishes come out of the dishwasher with spots.

For plants, hard water isn’t immediately toxic, but it causes problems over time. The minerals build up in the soil and form a white crust on the surface or around the drainage holes. You might also see white spots on the leaves if you’re misting with hard water.

The buildup can interfere with the plant’s ability to absorb nutrients. The soil’s pH shifts, and the plant starts to look nutrient deficient even if you’re fertilizing. I’ve had this happen with a few of my plants. The leaves turned yellow, and I thought I wasn’t feeding them enough. Adding more fertilizer just made the problem worse because it added more salts to the already salty soil.

The fix is to either switch to softer water (distilled, rainwater, or filtered), or to repot the plant in fresh soil every so often to get rid of the mineral buildup. I do a combination of both. I use tap water for most of my plants, but I repot them every year or two to reset the soil.

One thing to avoid: softened water from a home water softener. Those systems remove calcium and magnesium by replacing them with sodium. Sodium is even worse for plants than hard water minerals. If your house has a water softener, use water from an outside spigot that bypasses the softener, or use bottled water.

Research from the University of Minnesota Extension notes that hard water isn’t necessarily harmful to all plants, but sensitive species and long-term buildup can create issues. They recommend occasional leaching (flushing the soil with extra water) to wash out excess salts.

Above: The tools you need to fix this.

Best water for picky plants

Some plants just don’t tolerate tap water, no matter what you do. Calatheas, carnivorous plants, air plants, and some ferns need very pure water to thrive.

For these plants, I use distilled water or rainwater exclusively. I tried filtered water from a Brita pitcher, but it didn’t help much because most basic filters don’t remove fluoride or dissolved minerals. You need a reverse osmosis filter or a distillation system for that, and those are expensive.

Distilled water is cheap enough if you only have a few picky plants. I buy it at the grocery store for about a dollar a gallon. I go through maybe two gallons a week, which is ten dollars a month. It’s annoying to carry, but it’s worth it to keep my calatheas alive.

One question I see a lot: can you use distilled water for all your plants? Technically, yes. But it’s overkill for most common houseplants. Pothos, snake plants, and philodendrons do fine with tap water. Save the distilled water for the plants that actually need it.

If you’re serious about growing a lot of picky plants, you might want to invest in a reverse osmosis system. I haven’t done this yet because my apartment is small and I don’t have space under the sink, but I know people who swear by them. They produce very pure water, similar to distilled, and you don’t have to keep buying gallons at the store.

Another option is to mix water types. I’ve read that some people use half distilled and half tap water to dilute the minerals and chemicals. I haven’t tried this myself, but it makes sense if you’re trying to stretch your distilled water supply.

The bottom line is this: pay attention to your plants. If they’re getting brown tips, yellowing leaves, or white crust on the soil, water quality might be the issue. It’s not always about how much you water. Sometimes it’s about what you’re watering with.

I wish someone had told me this when I first started keeping plants. I would have saved my first calathea. But now I know, and hopefully you do too.

References

University of Massachusetts Amherst, Center for Agriculture, Food, and the Environment. “Fluoride Toxicity in Houseplants.”

University of Minnesota Extension. “Watering Houseplants: Quality and Quantity.”