Ph level of water

[Pdiscool]

Hey all, wondering how much the ph level of someone’s water affects the soil ph. I ask this because- according to my municipality my water had a ph of 6.5. Today I checked it with a vivosun ph meter, calibrated, and it read 5.0! Could this be lowering my soil ph? I do intend on checking my hr ph of my medium as well. Thanks all for input

[DrDraconian]

I would buy a gal of distilled water and test that with your pH meter to double check its accuracy. It would be HIGHLY unusual to be getting 5.0 pH water straight from the tap in any municipality in the continental US.

But yes, heavily acidic or basic water can have a large impact on the pH level that your tree experiences, but it will be modified by the buffering capability of your soil, so it won't be a direct correspondence.

In case your water really is a 5.0 pH, I would highly recommend adjusting it to get it closer to 6-6.5 if you can before watering your plants (unless you are watering one of the tropical plants that thrive in low pH environments).

[Sparky]

If you are saying that distilled water is a good way to check the accuracy of a pH test kit or meter because it has a pH of 7.0, I don't believe that is correct. I say this only because I remember reading that as soon as water is distilled it begins absorbing CO2 from the atmosphere which changes the pH and is no longer neutral. Please correct me if I am wrong.

[DrDraconian]

Sparky

Well apparently you are correct and I gave a bit of bad advice there. From what I was able to glean from a quick search:

"pH electrodes will NOT give accurate pH values in distilled or deionized water because distilled and deionized water do not have enough ions present for the electrode to function properly. The readings will drift and be essentially meaningless. If you want to test the accuracy of your pH electrodes, use pH buffers.
Tap water usually has enough ions present to allow a pH electrode to function properly. Because of this, tap water can be a good short term (~24 hours) solution for storage.
It is important to keep mind that water (distilled, deionized, or tap) is NOT “pure” (i.e., pH equal to 7). The moment it comes in contact with air, CO2 gas begins dissolving into it, forming carbonic acid. The actual pH, therefore, will typically be slightly less than 7."

I worked with de-ionized water in the lab, and knew that it had a fairly short lifetime before the water molecules began to dissociate and form ions, but I was not familiar with the process by which distilled water will acidify when exposed to ambient air. Thanks for the heads up.

[Pdiscool]

Interesting facts, thanks for that

[Pdiscool]

DrDraconian thanks for input!

[Vladimir]

Here are instructions for measuring soil mix pH: http://www.e-gro.org/pdf/2021-10-10.pdf

[Pdiscool]

DrDraconian something seemed fishy so I returned my unit and got a new one. I calibrated it and I immediately noticed how accurate it was out of the box. After fully calibrating it I was confident. I tested my tap water and it read 7.0! The other unit read 5.1

[DrDraconian]

Glad you were able to get that addressed. You should also be aware that if you fertigate (water your plants with water that has been treated with a water soluble fertilizer), the fertilizer can also affect the pH of the water. Most fertilizer will acidify the water a bit, but some can make it more basic. It usually not a big effect, but if you were starting with already marginal water it would be something you should take into consideration. With tap water close to 7.0 though, you should have no worries.

[Pdiscool]

Thanks!

[Vladimir]

I am not sure, but I suspect that the pH of the water has no lasting effect on the soil pH because of the soil's buffering capacity, i.e., resistance to change in pH.