The Carnivorous Plant FAQ v. 12

Q: About making purified water.

Utricularia inflata
Utricularia inflata
A: Pure water is essential for your carnivorous plants, because that is what they are adapted to in their wetland habitats. The tap water or well water in most houses contains too many chemicals, including calcium. Over time, these chemicals can kill your carnivorous plants or at the very least force you to repot more frequently because your planting medium is decomposing.

Here are several ways that you can try to make purified water. Most of these ways have been cooked up by people who do not know what they are talking about. The unsuccessful ways are pretty funny to me. Too bad they kill plants.

Ways that do not work

Aldrovanda vesiculosa
1)Letting water stand overnight in a pan or bucket
And what, precisely, is supposed to happen? Little water purification pixies will visit? I tell you what. Take a pan of water, put a dead rat in it and wait overnight. Next day I bet that rat is still there. Allowing water to stand overnight may allow some volatile chemicals to evaporate, but most of the things that will kill your carnivorous plants will still remain.

I think this method evolved from the aquarium trade, supposedly as a valid method to get chlorine out of municipal tap water before using it in a fish tank. But does this work even for this case? Unfortunately, since there are no explosives involved, I doubt MythBusters will cover this one.

2)Boil the water for a while
Other than ensuring your plants will not get dysentery, this will not do anything. You are trying to remove ions from the water, not organisms. Boiling may (may) drive off chlorine, but nothing else of importance. That dead rat will still be in the pot after you boil it. Boiled saltwater is still saltwater, and if anything is slightly more concentrated than before you boiled it!

3)Use coffee or "Brita" style pour-through filters
I do not know what these things do exactly, but I have tried a few experiments and found that they do not stop the salts that would accumulate and eventually kill your plants.

Ways that may work

Pinguicula macroceras
Pinguicula macroceras
1)Getting water right out of the tap
Some people live in places where the tap water or well water is gloriously pure and unprocessed. If you boil about 4 liters (1 gallon) of your tap water until it is completely gone, and see no white residue on the bottom of your pan, maybe you can use tapwater on your carnivorous plants!

2)Collect rain water
I used to do this. It was a serious pain in the bum. I would hose off my greenhouse before each storm to get the crud off it. I had a complicated system of gutters set up to guide the water into a big barrel. After each rain, the water still had all sorts of dust and stuff in it. I gave up after a while. If you collect rainwater off the roof of your house, do you have nasty tar shingles up there? I bet they would leach chemicals into your water. On the other hand, I had a friend in Tucson, Arizona, who had his own complicated system of gutters on his house, a couple of big storage tanks, and an interesting set of water pumps. He gathered all the water he needed this way. Sphagnum moss did not survive well in his greenhouse, and dead sphagnum fiber seemed to break down faster than normal, but other than that his plants did great.

Another person e-mailed me from the British moorlands to tell me that he gathered rainwater and it worked just fine. Good for him. And good for you if you share his luck.

3)Collect water from cooling units
Some people collect condensation water from their refrigerators. This is a pain in the bum, too. But it might work.

South Carolina
South Carolina
4)Make and operate a solar still
You could follow this route, as one FAQ-reader reminded me. However, I think that it would take a lot of tinkering. You would also want to keep the still fairly isolated from its surroundings so it would not get contaminated by airborne dust, acid rain, dog pee, or anything else that would degrade your water quality. I am sure there must be instructions on the web about how to make one, especially with all the nutty survivalists out there. (If you are a nutty survivalist, please do not take offense at my comments.) (Note to the non-survivalist FAQ-readers---you have to be careful about offending nutty survivalists---they can be nutty AND scary.)

Ways that do work

1)Get and maintain distiller or reverse osmosis unit
See the next FAQ entry for more information.

2)Buy purified water
See the next FAQ entry for more information.

3)Steal it from the lab where you work
Don't get caught.

Page citations: Rice, B.A. 2006a; personal observation.

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Revised: 2018
©Barry Rice, 2018