Discussion - How Much Does Your Tap Water PH Change On Standing?

It is a well known fact that water straight from the tap often has a different pH from tap water that has been allowed to stand for 24 hours. We usually ask for the pH of both when there is a problem.
In areas with acidic tap water, water companies often add something to the mains water to make it less acidic so the metal pipework does not corrode as quickly.
In areas with hard water, which usually goes with basic water, companies often add something to prevent limescale deposits in the pipework.
In both these cases, the pH will change when a sample of water is allowed to stand.

It would be interesting to see just how much this pH change can be.

I suggest that we all run a glass of tap water and test the pH immediately. Then leave it to stand for 24 hours and test again. Report the two values in this thread, together with an indication of the hardness of the water (hard, soft or middling will do) and the type of tester used.
This will give us an idea of the scale of pH change, and whether it is greater in hard or soft water.

Does this mean it is exactly 7.6 or somewhere above that?

Yes.

Mine goes from 7.4 to 7.2
GH 7-8, KH 2-3

I have done this test in the past, when I've been confused by my tank water values and how they differed from my tap water, because I thought I was doing something wrong to impact the tank.

Tap water pH is 7.0
After 48 hours pH is 8.4
17dH

Tests were done with the API kit.

I was just about to do this test... I still will, later on so I can do the repeat after work. But it just occurred to me that the ph drop might be related to the co2 content of the water. Is there anyone out there with appropriate test kit to identify co2 levels separately to pH? I also wonder if there will be a difference if I store the water for the repeat test in the test tube so the co2 can't gas off as much...

pH drop is one factor for changing pH. Do you have a container of some sort, even a spare beer glass 

I do have a container... but you've lost me!?!?

Getting half an hour of shaking done with an 8 week old at home is not going to be even remotely possible, whether I have the arm strength or not!!

My tactic is to... test initially then, leave 1 sample in a sealed container and 1 sample in an unsealed container for 24 hours before testing again. Not sure if ill see any difference... but ill try it nevertheless,!