Environment, Plants and Herbs

Is Bti water safe to drink? Or, Natural Pest Control for Paranoid Plant Keepers.

So, plants.

I have a lot of them. What witch hasn’t kept a pot of something on a windowsill somewhere, you know? In a previous incarnation of this blog, I talked about everything from trying to grow a rosemary bush, to collecting cacti, to that time my aloe plant absolutely would not stop reproducing. In short, I really like plants.

Unfortunately, my place doesn’t have any outdoor space to speak of. (None that I can use, anyway.) As a result, I have roughly one plant per 20 ft², and counting. The trouble is, not all of them are cacti — I also have a number of tropical plants that become really, really unhappy if they aren’t kept moist. I live in a very humid area, which they seem to enjoy, but…

Fungus gnats, though.

My poor, bedraggled fern…

Fungus gnats like moist soil. They deposit their eggs in it, and, before you know it, you’ve got masses of annoying, tiny gnats swarming around all of your plants. They’re not the only bugs that really dig on some wet dirt, either. When you combine plants that need to be kept moist with high humidity, it’s pretty much the ideal breeding ground for all kinds of tiny, annoying pests that are super enthusiastic about living in your pots.


I try to use natural pest control. My space is small, so I have to minimize my ability to inadvertently come in contact with pesticide. I also have two cats, so I really, really need to keep their exposure risk as low as possible. Since I don’t really have an outdoor hose/spigot I can use, any watering or diluting I do has to be done in either my kitchen or bathroom sink. Also, I try to avoid releasing any more pesticide/fungicide/herbicide into the sewer system than I absolutely have to.

My apartment is not really a place to bust out the big guns. 


All of this is to say, I became really curious about what happens if you accidentally drink water deliberately infested with insect-killing bacteria.

Don’t get me wrong, I don’t exactly have a compulsion to go shotgunning entire liters of Bti water, but I was curious. What if some of it gets on me? If I’m going to be working with it in my kitchen, what are the odds I’m going to come down with some kind of weird bug disease? If the water gets on my hands and I touch my face, is it going to start falling apart Jeff-Goldblum-in-The-Fly style?

Anyway, here’s what I’ve got:

What is Bti, anyway?

Bti is short for Bacillus thuringiensis israelensis (say that five times, fast). It’s a bacteria that is used as a natural form of insect control, because it produces toxins that certain insect species are susceptible to. Mosquitoes are one susceptible group, so you usually see Bti marketed in the form of mosquito dunks and granules to control their population.

How’s it actually work?

Short version is, the bacteria, bacterial toxins and all, are mixed into an inert matrix and molded into a kind of brick, granule, or donut shape. You dump ’em in some standing water, the bacteria are slowly released to begin doing their thing, insect larvae ingest them, the toxins make them stop eating, they die.

For houseplants, you can keep a mosquito dunk in your watering can. When you saturate the soil with the treated water, it kills some types of soil pests (like fungus gnat larvae) in much the same fashion. They take in the toxins, they die, voila.

How safe is Bti?

Here’s the complicated part — Bti pretty much only affects insects, and only specific insects, at that. Vertebrates don’t have the same digestive mechanisms insects do, so they aren’t affected. Some products even state that they can be used in bird baths and animal watering troughs to keep them from being a vector for mosquitoes.

Bti products have an abundance of cautionary instructions, including claims that they should not be used in water intended for human consumption. Swimming pools, however, seem to be okay. The EPA states that Bti poses no risk to humans or other, non-insect animals, but it’s best not to take that at face value for reasons I’ll get into in a moment.

So, is Bti safe in drinking water?

If Bti products are safe to use in swimming pools, and the EPA says that it poses no risk to humans, why shouldn’t Bti products be used in drinking water? There are a couple of reasons:

  • Bti products aren’t just Bti. They are also made up of proprietary inert ingredients and binding agents that may not be great for human consumption. The EPA’s ability to say that Bti itself doesn’t pose a risk to humans does not necessarily transfer to a product in which Bti is one of many ingredients.
  • The producers of Bti products did not shell out the astronomical sums of money required to perform a full-scale human safety assessment. Properly performing product safety tests on human subjects is difficult, expensive, and takes a very, very long time. For liability reasons, they cannot guarantee your safety if you chug their stuff.
  • Bti is usually tossed into stagnant water. The producers of Bti products don’t want to be liable for someone who gives themselves cholera because they thought a couple mosquito dunks would make their water safe.
  • Some Bt strains can produce beta-exotoxin, which is toxic to basically everything. Strict quality control guidelines have to be in place to make sure that these bacterial strains and their toxins don’t contaminate finished products. Bt products intended for Canada, Europe, and the U.S. are legally required not to contain beta-exotoxin.

That said, the EPA isn’t the only organization with things to say about Bti. The WHO has a whole PDF about it for the purposes of developing quality guidelines for drinking water. In it, they conclude:

Bti itself is not considered to pose a hazard to humans through drinking-water. Therefore, it is not considered necessary or appropriate to establish a guideline for it. However, the absence of contaminating bacteria or other impurities cannot be assured under currently allowed production practices and post-production testing requirements as quality assurance and quality control measures. Therefore, stricter and more comprehensive requirements for production and post-production testing and better defined criteria for purity and safety are recommended to minimize human health risks from possible drinking-water exposures.

Short version: Bti is safe. The other stuff that ends up in water along with it may not be. We need stricter QC guidelines and better production methods before we let anyone go around drinking it.

But can you drink Bti treated water, or not?

I mean, I wouldn’t.

Ultimately, if it is only Bti in the water, it’s probably alright. However, there is absolutely no way to guarantee that in your typical home/garden setting. Because of the small potential for quality control issues (recalls can happen, even for innocuous products) and the fact that Bti is used for stagnant, nasty water, it is not a great idea to drink it. So, while you don’t need to bundle yourself in a HAZMAT suit every time you so much as touch the stuff, you should still wash your hands after using it, don’t inhale the dust, and avoid hosting any homebrewed Bti keggers anytime soon.


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