Can distilled water be harmful if used regularly?

[powderherface]

Hello! The water in my area is really hard, and the filter I own doesn't do the best of jobs. So I've decided to conduct an experiment: get my hands on pure (distilled) water, and use my 'weakly, weekly' fertiliser (which contains some Calcium & Magnesium) to balance this out. All my orchids are mounted, in a greenhouse environment.

This leaves me with a few questions & options:

1. in the 6 days a week, when I'm not fertilising, is there any biological harm I can do to the plant by only offering it pure water on those days?

2. would a daily fertilisation (at x7 the current dilution, in distilled water) actually be better & closer to what epiphytes may get naturally?

3. or perhaps, somewhere in between, e.g. every other day (further diluted x3.5), with a distilled water flush in between every water?

Would be great to hear people's thoughts & wisdom on this! I lack the plant science background to differentiate between these options.

PS: am aware of alternative pure-ish waters (RO, even rain water) -- but distilled was the easiest to buy where I leave.

[Blueszz]

Welcome, good question!

Pure distilled water should theoretically have a neutral pH of 7.
But just like reverse osmosis water (often used for fish tanks and some local fish stores sell it), distilled water quickly absorbs CO₂ from the air, which makes it slightly acidic.

As a result, the pH usually falls between 5.0 and 6.5. When I Google pH 5 and orchids pH 5 might be too low for instance because it can damage root tips. Also I read about becoming essential nutrients less available. But I don't understand why.

If it was me I would remineralize distilled/RO water with each watering using Rain Mix from Akerne in Belgium. I'm sure the owner Kenneth is willing to help with the correct dose of this fertilizer when used with each watering.

But member Ray probably can help you with this too. I'm sure he'll chime in.
I highly recommend reading articles on his website (Free Information button). You can find his website here: First Rays LLC

[powderherface]

Thank you! Rain Mix is precisely the fertiliser I currently use weekly (previously with filtered water), so I am very pleased to see it recommended.

Interesting about the pH lowering, that's really useful to know. Re-mineralising with this mix does seem sensible. I suppose the danger might be gradual salt buildup, but maybe that's remedied through drenching with rain water every now and then (I can't collect enough to use rain water regularly unfortunately).

Thank for the link, I'll check that out.

[Roberta]

The pH lowering is not a problem. The pH in the medium will be fine (measure what runs through the mix, not what is going in) That bit of CO2 has no buffering capacity at all. The only concern with pure water is that you need to add calcium and magnesium. A fertilizer designed for tap water won't have it (read the label and it will tell you) so either use a forumula that has added calcium and magnesium because it is designed for pure water (such as Akerne Rain Mix) or use a seperate cal-mag product. It sounds like the fertilizer you are using already has cal-mag in it.

Filters don't remove solids from water. Only reverse osmosis or deionizer (or distillation) will do that.

If your water is hard, the plants will be delighted with the pure water. You can also use rain water (which is what they get in nature)

[Blueszz]

Originally Posted by Roberta

The pH lowering is not a problem. The pH in the medium will be fine (measure what runs through the mix, not what is going in) That bit of CO2 has no buffering capacity at all. The only concern with pure water is that you need to add calcium and magnesium. A fertilizer designed for tap water won't have it (read the label and it will tell you) so either use a forumula that has added calcium and magnesium because it is designed for pure water (such as Akerne Rain Mix) or use a seperate cal-mag product. It sounds like the fertilizer you are using already has cal-mag in it.

Filters don't remove solids from water. Only reverse osmosis or deionizer (or distillation) will do that.

If your water is hard, the plants will be delighted with the pure water. You can also use rain water (which is what they get in nature)

There is no medium, the plants are mounted. That's why a low pH can be a problem imho.

It's the distilled or RO water that doesn't have buffering capacity and that is why CO2 can have such an impact. At least, that is the theory I always worked with in my aquarium hobby. With RO water you can lower the pH of fish tank water. It's often mixed with tap water to lower the pH.

[Roberta]

Don't worry about the pH of the pure water. Epiphytic orchids evolved in a pure-water environment (rain) with very minimal amounts of anything else (what might dissolve as the water trickles through the forest canopy) Some are more forgiving than others of the "liquid rocks" that may come out of the tap, but if they can get pure water, they'd much prefer it.

[Blueszz]

Originally Posted by Roberta

Don't worry about the pH of the pure water. Epiphytic orchids evolved in a pure-water environment (rain) with very minimal amounts of anything else (what might dissolve as the water trickles through the forest canopy) Some are more forgiving than others of the "liquid rocks" that may come out of the tap, but if they can get pure water, they'd much prefer it.

Agree and never looked at it this way.

[estación seca]

The carbonic acid produced by carbon dioxide in pure water is very low in concentration and quickly neutralized by almost any organic matter, like leaves or roots. It's not a concern with any kind of plant. Stronger acids like hydrochloric, sulfuric or acetic (vinegar) might damage plants, depending on the concentration.

[Henry]

Using Ray's calculator for one liter of our spring water I got:

"Ray - I have found that applying a solution containing 75-125 ppm nitrogen per week is a great level to sustain growth and blooming."

So...
.85 gram/liter of Rain Mix powder
ppm N 100 right in the middle!
ppm P 10
ppm K 97

[Ray]

Originally Posted by powderherface

1. in the 6 days a week, when I'm not fertilising, is there any biological harm I can do to the plant by only offering it pure water on those days?

2. would a daily fertilisation (at x7 the current dilution, in distilled water) actually be better & closer to what epiphytes may get naturally?

3. or perhaps, somewhere in between, e.g. every other day (further diluted x3.5), with a distilled water flush in between every water?

1. There is absolutely no issue with the use of pure water. As Roberta mentioned, rainwater is pure - from nature’s distillation process.

2. Very dilute and very frequent mimics nature and is the best way to feed. Think of the food analogy for people - it is healthier to eat several low-calorie meals rather that stuffing yourself with one, large one having the same total calories.

3. With the low-concentration fertilizer solution buildup will be minimal, so a thorough pure-water flushing once a month is likely sufficient.

Originally Posted by Blueszz

Pure distilled water should theoretically have a neutral pH of 7.
But just like reverse osmosis water (often used for fish tanks and some local fish stores sell it), distilled water quickly absorbs CO₂ from the air, which makes it slightly acidic.

As a result, the pH usually falls between 5.0 and 6.5. When I Google pH 5 and orchids pH 5 might be too low for instance because it can damage root tips. Also I read about becoming essential nutrients less available. But I don't understand why.

The equilibrium pH of pure water and the current atmospheric carbon dioxide level is about 5.7-5.8.

Low (or high) pH may-, or may not be harmful:

pH is a measure of the concentration of free H+ ions in a solution, but can be thought of as a ratio. If the H+ and OH– ion concentrations are equal, there are no “free” H+ ions and the pH is 7, neutral. An excess in H+ results in a low, acidic pH and an excess on OH– gives a high, basic pH.

As it is a ratio, if one solution had 100 H+ ions and 1 OH– ion, and another solution had 100,000,000,000 H+ ions and 1,000,000,000 OH– ions, the pH of the solutions would be identical, at 6.0.

Not too surprisingly, the first solution is very weak, so won’t have an appreciable effect on plants and the pH balance can be affected by almost anything. That second solution, on the other hand, is much stronger, so can affect the plant and will be much more resistant to pH change.

There are two, totally different, but equally unimportant aspects of pH on nutrient availability and nutrient uptake.

Availability is related to cation exchange capacity (CEC) in soils, affected by microscopic particles of clay and organic matter. Orchid media - and certainly slabs - have almost no CEC, so if a nutrient is in solution, it’s available.

Within the range of pH that the plant, the substrate, and the microbes therein keep things, pH has negligible impact on uptake.