[yecatsk3]

Why would spring water that has been stored for six months in a bottle test differently than in the field only for Ca+ and HCO3-? And also have an increase in pH?
Initial analysis for Ca2+ was 93mg/L down to 22mg/L. HCO3- was 556 mg/L down to 297 mg/L. my pH increased from 7.4 to 8.4.
None of the other components for the water have changed.
I think the lowering of HCO3- might have to do with the reation of CO2 in the water which would form carbonic acid, which I think would be the cause of the increased pH. But Im at a loss for the Ca2+. Any help would be awesome. I'm a little confused.

[Borek]

Two problems with long stored samples. First, depending on what you store them in, they can leach additional substances from the bottle. This can lead to either detection of these substances, or to unpredictable reactions changing the solution composition.

Second, if they are allowed to exchange gases with the atmosphere, amount of CO₂ dissolved can change. In your case it looks like you have lost some of the CO₂:

Ca²⁺ + 2HCO₃^- CaCO₃(s) + H₂O + CO₂

That would be consistent with all three observed changes - rise of pH and lowering of concentrations of Ca²⁺ and HCO₃^-. Settled down CaCO₃ precipitate can be difficult to spot, as it can just leave a thin, matte (I hope that's a correct word) layer on the bottle surface. (This is the same reaction that is responsible for karst feature development).