Watering with dehumidifier water? Hard tap water questions

[Phalaenoptics]

Hi all!

My tap water is very hard. While my phals are growing happily, I would like to be better to them - especially if in the future I might want plants that require mineral-free water.

I do want to eventually get a rainwater butt/collector for the garden but that's not in the cards right now.

I do have a dehumidifier in the basement, which is very humid. I've heard you can water with dehumidifier water, but is it safe? Whenever I empty the dehumidifier, it seems to collect some sort of black sediment at the bottom, probably from dust and particles in the air. I'm wary of fungal and mold spores being particularly high in that water, since it's in the basement.

alternatively, is it possible to pH adjust hard tap water by adding an acid? 🤔

[Ray]

The problem with very hard water is not necessarily the pH as much as it is the alkalinity, which is the resistance to pH change upon the addition of acids. Even if you correct the pH, those alkaline minerals are still present in the water, and will drive the pH of the medium upward, ultimately becoming toxic.

I would definitely use the dehumidifier water. Just keep the collector clean.

Also, you can get an inexpensive, portable RO system from Amazon and fill up jugs knowing it's pure.

[Roberta]

How hard is "very hard"? Phalaenoptics, where are you located? I am in southern California. While I have found RO to be helpful and even necessary for some of my cloud-forest orchids, everything else gets city water, which is high in calcium bicarbonate, with a well-buffered (stubbon) pH of about 7.8 . When I fertilize I use the pure water for everything, and the MSU Cal-mag pure water formula, so I end up with a good pH. But for the general watering, I have seen no ill effects on Catts, Cymbidiums, Oncidiums, Phals, Paphs (which actually prefer it according to Brandon Tam of the Huntington). I have also never seen a calcium deficiency, which seems to be an issue in some places that don't have high calcium in the water.

[Phalaenoptics]

Originally Posted by Roberta

How hard is "very hard"? Phalaenoptics, where are you located?

I am in New England, in a Massachusetts suburb. I've looked up our city's water report in the past but it mentioned nothing about water hardness.

However, I assumed it was hard because of how it felt on the skin when I showered, as opposed to the water I was used to in the city. I also noticed when I watered my plants that some splashes would dry white on the leaves, so I naturally assumed mineral deposits.

Now that I did some further googling, I found that our town's water supply is actually "soft"! It is 16 ppm, or 1 gpg. It is treated to have a PH of 9.0-9.5.

I don't know what to do with this information. Experts, please advise!

[Roberta]

Your tap water is lower TDS than my RO! Now, the "gotcha" is that if they used sodium hydroxide for the pH adjustment, sodium is a bad actor for plants. But the dose makes the poison. If the overall total dissolved solids is that low, the amount of sodium is probably quite small. And water that pure has essentially no buffering capacity - if you measure the pH of fertilizer water with 1/2 teaspoon per gallon of, for instance, 20-20-20, my guess is that the fertilizer will easily lower the pH into the 5.5-6.5 range that is ideal for uptake of minerals. Also, with water that pure, you'll probably want to supplement calcium and magnesium. Search for notes from Ray, his posts include some excellent information.

[Phalaenoptics]

Thanks for all your help, Roberta! I definitely learned so much today!

I've got a pH tester I have yet to put to use (since I wanted to get good at growing the plants first) but now I see some experiments are in order.

I did notice that some of my phals' leaves were a bit floppy, despite showing no other signs of distress. I looked it up and suspected possible calcium or magnesium deficiency. I've been adding a tiny bit of Cal-Mag with my last 2-3 waterings because I didn't want to overdo it/cause some sort of fertilizer burn. Hopefully will see some improvement now that I know where to direct my care!

Thanks again!!

[estación seca]

Yes, use your tap water!

In addition to what Ray and Roberta mentioned, be sure to use a fertilizer with micronutrients. Your tap water lacks all the minerals plants need: nitrogen, potassium, phosphorus, sulfur, iron, manganese, magnesium, calcium, copper, boron, iron. If you use Epsom salts for magnesium supplementation, your plants will get enough sulfur.

And don't mix calcium supplements with other fertilizers. Calcium can form insoluble compounds with other things in the fertilizer. Use them at different waterings.

[Phalaenoptics]

Thank you for the tip about Calcium, ES!

I bought some of Bill's Best fertilizer and Plant Potion #9, from here: Collections – Bulbophyllums.com

I've been using them sparingly (at quarter strength dilution) maybe once a month?

I also have some Superthrive and orchid probiotics from Repotme, and KelpMax (which I have yet to apply).

Basically, I'm all potioned up, I just haven't figured out any sort of routine hahaha

[Ray]

Originally Posted by Phalaenoptics

I also have some Superthrive and orchid probiotics from Repotme, and KelpMax (which I have yet to apply).

If the Superthrive is old or has been allowed to get warm, it is chemically inactive.

It is a root-growth stimulant, but overdosing can result in flower deformities. KelpMax is a general plant stimulant, but it also tremendous at stimulating root growth, but is totally safe to use. Use one, not both.

When you run out of the privately-labeled Quantum Orchid, get the identical product - Quantum-Total - at a much cheaper price.

[Phalaenoptics]

Thank you everyone! I have a lot to learn about ferts and supplements (and a lot of experimentation ahead of me, I'm sure)

I appreciate everyone's sage advice.