I'm sort of professional at this and couldn't resist commenting. Honestly -- pH 6.8 and pH 7.8 are as near dammit the same as neutral. Drinking water from limestone areas can be on the higher pH side 7.5-7.8 because of bicarbonate. But the pH of water can vary widely according to the smallest of changes. As you may know the pH is minus the log of the concentration of H+ ions - and 10 E-7 molar really isn't a very high concentration (0.1 micromoles/ litre = a fraction of a microgram) and this number can be significantly shifted by adding correspondingly absolutely tiny amounts of any substance that either dissociates to provide protons (acids) to take pH down or that binds protons (bases) to take pH up.
The pH of water will shift down somewhat even if you just blow through it- or just over time -because the carbon dioxide in your breath will dissolve to make carbonic acid and potentially take the pH down to 6 or so.
Virtually anything you eat -or have eaten - and anyway just mouth, stomach and intestinal fluids - will instantly and massively change and dominate the pH of any water you ingest anyway - because the pure water you drink immediately then becomes a complex solution of many substances which then together control pH.
Even more so - and fortunately - the pH of our blood, lymph and the cytoplasm within every cell of our body is tightly controlled to within a very narrow range around 7 by our metabolic biochemistry.
So - while there are few things that I would stick my neck out and say that I am certain of -- I am certain that the pH of drinking water is not a variable that anyone should worry about too much.
Anyway if you won't accept my wisdom on this please take it from my cat - he happily drinks our pH 7.5 tap water --but equally laps up the rather nasty water in the pond which I think is relatively acidic at 6.0 or so -- but he is still ghoing strong at 18 or so.
Tim
