It’s well-known among carnivorous plant growers that the plants require purified water. But what does “purified” mean, and why is it so important for healthy plants? Strap on your goggles, and let’s dive into this water topic.

What is purified water?

Purified water is water that has gone through advanced filtration to remove impurities and contaminants. When we talk about all carnivorous plants, the impurities we’re concerned with are mostly in the form of minerals. Minerals = bad. Techniques to purify water include carbon filtration, collecting rainwater, reverse osmosis, distillation, and deionization. Let’s take a look at each technique, discuss pros and cons, and determine:

  1. The best purification method based on quality and quantity of water
  2. What method is easiest to setup and maintain
  3. What method is cheapest to setup and maintain
  4. And finally, determine the best overall method to keep your plants happily hydrated!

Wait, why do carnivorous plants even need purified water?

its what plants crave

Many carnivorous plants evolved in nutrient poor soils and root systems adapted to low-mineral availability. The thinking goes that this is a primary factor in the onset of carnivory – a means to supplement the dearth of nutrients by capturing them from the environment via insect prey. Adapted roots are hypersensitive to excess minerals as a result.

Since you’re likely growing your carnivorous plants in low-nutrient soils like sphagnum moss, peat moss, perlite, horticultural sand, etc, the only remaining way to get excess minerals into the soil are via water. So, it would make sense that water needs to be low in dissolved mineral salts, as indicated by parts per million (p.p.m.) or total dissolved solids (t.d.s.), to keep overall root health hunky-dory.

Water with one hundred p.p.m. and below is the target for healthiest carnivorous plant growth. Anything more, and plants will show symptoms of stress in the form of gnarled foliage, browning or burned leaves, or stunted growth. Since many carnivorous plants require constantly moist soils and stand in water because of the water tray method, minerals build up over time, rotting roots and damaging the plant.

When exposed to seasonal rainfall, outdoor plants can do ok with total dissolved solids up to 160 p.p.m. Rain is mother nature’s purified water, and acts to leach excess minerals from the soil. I’ve lived in some areas, like Berkeley, California, where water from the tap is good enough to give directly to the plants, but this is very rare, and using the methods outlined below to condition your carnivorous plant water is required for most growers. Keep in mind that you can measure your t.d.s. with an inexpensive p.p.m. meter from Amazon if your water quality is suspect. Most p.p.m. meters use the electrical conductivity of water as a means to determine impurity levels. Since minerals ions are either positive (cations) or negative (anions), they transmit electrical current when electrodes are placed in the water. The presence of more ions means higher conductivity, and the higher your p.p.m. reading. A higher p.p.m. reading is therefore indicative of more minerals in your water. Isn’t science fun?!

In addition to total dissolved solids, water pH (potential for Hydrogen – a measure of alkalinity/acidity) should be neutral at around 7.0. Limestone in groundwater can make water too alkaline, and some cities add lime to acidic water to slow the corrosion of municipal piping. You can test the pH of your water with simple, inexpensive test strips from Amazon (also often found at aquarium and pool supply stores). Do not exceed a pH of 8.0 (alkaline water) for your plants.

Carbon Filtration

Carbon filtration

As the name suggests, carbon filtration uses a carbon-based filter to strain particulate from water. It’s great at neutralizing smell and taste, removing large-to-medium particulate, and generally yields good drinking water. However, this filtration method doesn’t remove enough minerals to be used for watering carnivorous plants. You’ll need finer filtration to get the quality of water needed.


rainwater collection

Free, all-natural, and pure, rainwater is a great option for watering your carnivorous plants. Natural hydrologic cycles filter out most water impurities. You’ll simply need to collect rainwater in containers that can be siphoned from at a later date. If rainwater will be stored for a long period of time, consider opaque containers that block out light that would otherwise encourage algae and bacterial growth. If stored outside, consider UV-resistant containers that won’t age and crack while sitting in sunlight. Also note that water stored in darker containers that absorb light can heat up, so cool it down to avoid cooking your plants.

If collecting rainwater from a house gutter system, make sure that the roof hasn’t recently been treated with moss inhibitor, fire retardant, or other chemicals that could harm your plants.

Reverse Osmosis

reverse osmosis

Reverse osmosis, or RO systems, use high pressure to press water through semipermeable membranes. These membranes are, themselves, comprised of multiple layers that filter out finer-and-finer particulate. Common thin film composite (TFC) membranes are made by stacking a woven fabric polyester base with a polysulfone porous layer, and a polyamide layer. They are so fine that they filter out anything more than a few microns wide – most bacteria, organics, and pesky root-damaging minerals are removed. RO systems hook up to tap water piping and store purified water in tanks that commonly live under a kitchen sink for easy accessibility via sink-top spigots.

Reverse osmosis systems have come down in price over the last decade, and good ones can be purchased for less than $200 on Amazon, here. This particular unit can produce up to 75 gallons of usable water in one day. These types of residential units are the most common, convenient, and economical way to produce enough water for a small-to-medium sized collection of carnivorous plants – plus they produce excellent drinking water!

There is one downside to RO systems – they produce wastewater. It’s for a good reason, though. With standard filtration, contaminants get trapped in the filter, build up over time, and reduce water throughput and efficiency by clogging the system. With Reverse Osmosis, cross filtration solves this problem by using water to wash away contaminant build up. This water ends up draining out of the system, and many RO systems only produce one usable gallon per three gallons of input. Thankfully, we’re out of the drought here in California, but if you’re water conscious, this is important to understand.

Every couple of years, you’ll need to replace the Reverse Osmosis membrane as the pores expand and allow more impurities to pass through. You can use the previously-mentioned p.p.m. meter to determine the quality of water and gauge if a replacement membrane is necessary. Or just, you know, follow the instructions on the box. 😊

Water Distillation

water distillation

Water distillation mimics natural hydrologic cycles in which water evaporation separates out all impurities. With distillation, heat is applied to boil water into steam. During this process, minerals and other contaminants that have a higher boiling point than water (at 212°F, 100°C) can’t hang with water as it evaporates, and are left behind. Steam is then condescend (mimicking cloud formation), and liquid water can then be extracted and collected (mimicking rainfall) in a tank within the distillation device. This results in water that is around 99.9% pure. It’s hard to argue with a method that has supported life for billions of years.

With that said, distillation itself isn’t perfect. For instance, volatile organic compounds/synthetic chemicals with lower boiling points than water will not be removed during distillation. That said, many of these compounds are also small enough to sneak through reverse osmosis filters. I wouldn’t worry about this too much, though, as your tap water shouldn’t contain things like chlorine, and municipal filtration removes many/most of these compounds before the water reaches you. Theoretically, at least.

Residential distillation units also tend to produce smaller quantities of purified water at around 5 gallons per day at their peak (if you’re emptying them at the end of a distillation cycle to immediately trigger another cycle). While sufficient for smaller carnivorous plant collections, you may find yourself quickly outgrowing affordable countertop distillation units.

Please note that simply boiling water in a pot won’t yield the same results as distillation. There is no net loss of minerals as a result of adding heat to boil water. Quite the contrary, water lost to steam will result in the remaining liquid water within the pot having higher mineral concentrations. This will be worse for your plants. Remember, it’s the collection and re-condensing of steam – a purified, gaseous form of water – that will give you purified water.

Like reverse osmosis systems, water distillation systems have come down in price over the last decade, and reputable ones can be had for about $200 on Amazon, here.

Water Deionization

water deionization

Deionized water (DI water) will be some of purest you can produce. Frequently, deionized water impurities are measured in the parts per billion rather than the more common parts per million. When a p.p.m. meter reads “1,” it’s a sign that your water deionization system is waning. Remember, carnivorous plants enjoy water at 100 p.p.m. I’ve never tried watering carnivorous plants this way as it’s super-duper overkill, but theoretically should work. Probably worth a future experiment.

This water is so pure that it can actually leach contaminants, metals, etc, out of pipes and other surfaces it comes into contact with (not a good thing). If you drink quantities of it (which you won’t want to do, because it can smell funny), it will damage your intestinal mucosae and cause mineral deficiencies. It is, in general, not a good source of potable water. It is great for washing your car as the water is so pure that it dries without leaving water spots. Deionization water is also frequently used in scientific experiments when sensitive laboratory instruments are needed to detect chemicals at minute concentration levels.

Yah, like I said. It’s a wee smidge overkill.

That said, allow me to elucidate the inner workings of deionization. It’s fascinating. DI filters go by multiple names, but we’ll use “Ion Exchange” since this most clearly describes the means employed to purify the water.

Ion Exchange filters swap negative hydroxyl molecules and positive hydrogen molecules for the negative and positive contaminant molecules found in your water. It’s an equivalent exchange where negative chemicals (like iodine) exchange places with the hydroxyl molecules and positive chemicals (like calcium) exchange places with hydrogen molecules. Simply put, this swaps out the bad stuff for good stuff, leaving you with pure H2O.

If you’re up for a somewhat expensive experiment, you can pick up a residential-grade water deionization system here. Wash your car with it, water some carnivorous plants with it, and let us know how it goes in the comments below! As a bonus, this unit comes with a built-in t.d.s. meter to measure water purity, so no need for an external meter. A downside to this unit is that they recommend a filter replacement after 400 gallons – far short of reverse osmosis filter requirements. That said, deionization systems produce water of such a purity that you may be able to ride the filters past 400 gallons if p.p.m. stays below 100.


I mentioned I’d break these down for you based on these important criteria:

  1. The best purification method based on quality and quantity of water
  2. What method is easiest to setup and maintain
  3. What method is cheapest to setup and maintain
  4. And finally, determine the best overall method to keep your plants happily hydrated!

Right off the bat we can filter out (see what I did, there?) carbon filtration since it doesn’t meet your carnivorous plant’s standards. We’re left with rainwater, reverse osmosis systems, water distillation units, and deionization systems as options.

1. Best quality and quantity of purification:

Rainwater will be just about tied with distillation for purity of water, but you’re limited to the amount of rainwater you can collect.

Reverse osmosis is not the purest option, but produces great water that’s perfectly fit for your carnivorous plants, and outputs significantly more water than common distillation units, making it better for a growing carnivorous plant collection.

Distillation is going to get you water purer than reverse osmosis, but common household units yield small quantities of water per day.

Deionization will produce the purest water (almost to a fault), and while daily yields can be high, lifespan of filters limits overall yields

Winner: Reverse Osmosis

2. Ease of setup and maintenance:

Rainwater is easy to collect via existing home gutters. Setup requires no special plumbing or modifying under-sink areas. It may require light gutter re-engineering depending on your current setup. Maintenance is low.

Reverse osmosis systems sit under your sink and dispense water at the flick of a button. Setup is more complicated and involves hooking it up to your pipes. Maintenance is low, with membranes needing to be replaced every few years.

Distillation units just sit on your counter, and you fill them with water when they run low. Setup is minimal. Maintenance is medium, requiring units to be occasionally cleaned.

Deionization units can hook up to hoses for super-simple setup, but will require semi-frequent filter replacement.

Winner: Rain water

3. Best setup and maintenance price:

Rainwater – you can’t beat free (dependent on the cost of your rainwater collection reservoir), but there’s a good chance you’ll still need to invest in another purification method to supplement limited seasonal collection of rainwater. For this reason, we should factor in the cost of an additional system on top of the raw rainwater collection costs.

Reverse osmosis systems are a little less expensive than distillation units, and have a lower cost per gallon price point. Over time, filter replacement costs are low.

Distillation units are a little more expensive than RO systems, but if you look at the cost per gallon of purified water over time, they’re much pricier.

Deionization units probably the most expensive option on the list due to high upfront costs, and frequent, expensive filter replacements.

Winner: Reverse osmosis

4. Overall winner:

Rainwater + Reverse osmosis – a combo?! Isn’t that cheating? Of course not! Combine the low-costs of rainwater with the high-output and accessibility of reverse osmosis, and you’re set! Rainwater balances out the environmental downsides of RO wastewater, and RO supplements the seasonal availability of rainwater. It’s a great 1-2 punch to keep your carnivorous plants quenched with pure, inexpensive, water. Bonus: reverse osmosis makes great drinking water for you and your entire family – even those of the non-Plantae variety.

carnivorous plants in purified water