RO water pH question

This season I’ve been using RO water from a local store. The pH consistently comes out 8.0+ out of the jug. Is that normal?


RO water has no pH. pH is a measure of charged ions in water. RO water has no ions present and therefore it cannot have a pH. The measurement is invalid until you add dissolved solids to the water. Only then can it have a pH.


If the water is truly reverse osmosis then the pH will creep down as carbon dioxide is absorbed into it. But it has so little parts per million of anything in it you can ignore it. Most of us don’t even bother to check it as no pH meters can give you a true measure of RO water unless you pay a thousand dollars for a laboratory grade meter. And its not necessary to adjust Distilled either as its basically the same.

1 Like

Great point. As CO2 is absorbed into RO or distilled, it is converted to carbonic acid in the water. Once PPM reaches 100 or so, then a pH measurement is possible.


:point_up:what they said

1 Like

Thanks for the response. If I’m getting a pH reading is it just a false reading? I ph balance water when I use nutrients, but I have used the water untreated and I’ve had a problem with stunted plants this season.

1 Like

Yes, In anything below 100 PPMs the reading is suspect.
My RO is around 5 to 10 PPMs and my meter bounces all over if I try to check pH.

Thank you for taking time for the comments.

I’m going to try a different water source and see if I get similar results.

Just FYI and kinda useless information. But I’m pretty involved with planted FW aquariums and the max CO2 for non injected water (exposed to atmosphere) is between 2 and 4ppm CO2.

Add calmag to your RO to get it up to 250-300 ppm. It then becomes PH stable and can be used to adjust your soil. PH unstable water will become adjusted by the soil instead.

1 Like

I checked my tap water with a test stick

-total hardness ppm= 1-100 ppm range
-chlorine, total=0.25ppm

Would that be safe to use without adjustments?

If the TDS is under 100 and no chlorine present you can just water without adjusting PH. The medium will correct that immediately.

Adding a few drops of H2O2 to your tap water will dissipate chlorine and chloramines within minutes.

1 Like

Awesome, thank you

1 Like